Peanut Butter Banana Baked Oatmeal Casserole

Quick Recipe Version (TL;DR)

• Yield: 10 servings
• Prep Time: 20 minutes
• Cook Time: 35 minutes
• Total Time: 55 minutes

Quick Ingredients

• Cooking spray or butter (for greasing pan)
• 3 cups old-fashioned rolled oats
• 1/2 cup chopped roasted peanuts, plus 2–3 tbsp for topping
• 2 tsp ground cinnamon
• 1 1/2 tsp baking powder
• 1/2 tsp fine salt
• 2 1/2 cups milk (dairy or unsweetened non-dairy)
• 1 cup mashed very ripe bananas (about 3 medium)
• 2 large eggs
• 1/2 cup creamy peanut butter, plus 2 tbsp for drizzling
• 1/3 cup pure maple syrup or honey
• 2 tsp vanilla extract
• 3 tbsp melted unsalted butter or coconut oil
• 1 medium banana, sliced, for topping

Do This

• 1. Heat oven to 375°F (190°C). Grease a 9×13-inch baking dish.
• 2. In a large bowl, combine oats, 1/2 cup chopped peanuts, cinnamon, baking powder, and salt.
• 3. In another bowl, whisk milk, mashed bananas, eggs, 1/2 cup peanut butter, maple syrup, vanilla, and melted butter until smooth.
• 4. Pour wet mixture into dry ingredients; stir until evenly combined. Let sit 5 minutes to thicken.
• 5. Spread batter into the prepared pan. Top with banana slices, extra peanuts, and drizzle with 2 tbsp melted peanut butter.
• 6. Bake 30–35 minutes, until set in the center and golden around the edges. Cool 10 minutes, slice, and serve warm.

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Why You’ll Love This Recipe

• Hearty, stick-to-your-ribs breakfast that feels like dessert but is packed with oats, peanuts, and bananas.
• Perfect for feeding a crowd or for make-ahead breakfasts all week long.
• One pan, simple ingredients, and very little active cooking time.
• Flexible and forgiving: easy to make dairy-free, adjust sweetness, or add fun mix-ins.

Grocery List

• Produce: 4 medium ripe bananas
• Dairy: 2 1/2 cups milk (cow’s milk or non-dairy), 2 large eggs, 3 tbsp unsalted butter (or use coconut oil)
• Pantry: Old-fashioned rolled oats, creamy peanut butter, roasted peanuts, pure maple syrup or honey, vanilla extract, ground cinnamon, baking powder, fine salt, cooking spray or neutral oil for the pan

Full Ingredients

Main Baked Oatmeal

• Cooking spray or butter, for greasing the pan
• 3 cups old-fashioned rolled oats (do not use quick or instant oats)
• 1/2 cup roasted peanuts, roughly chopped (salted or unsalted)
• 2 tsp ground cinnamon
• 1 1/2 tsp baking powder
• 1/2 tsp fine sea salt or table salt
• 2 1/2 cups milk (2% dairy milk or unsweetened almond/oat milk both work well)
• 1 cup mashed very ripe bananas (about 3 medium bananas, well spotted and soft)
• 2 large eggs
• 1/2 cup creamy peanut butter (stirred well if using natural)
• 1/3 cup pure maple syrup or honey
• 2 tsp pure vanilla extract
• 3 tbsp unsalted butter, melted and slightly cooled (or melted coconut oil for dairy-free)

Topping & Serving

• 1 medium banana, thinly sliced
• 2 tbsp creamy peanut butter, melted for drizzling
• 2–3 tbsp roasted peanuts, roughly chopped
• Optional: extra cinnamon, a drizzle of maple syrup, or a splash of milk/yogurt for serving

Step-by-Step Instructions

Step 1: Prep your pan and oven

Preheat your oven to 375°F (190°C) with a rack in the center. Lightly grease a 9×13-inch baking dish with cooking spray, butter, or a thin layer of oil. Make sure you get into the corners so the oatmeal releases easily later. Set the dish aside while you mix the batter.

Step 2: Mix the dry ingredients

In a large mixing bowl, add the 3 cups oats, 1/2 cup chopped roasted peanuts, 2 tsp cinnamon, 1 1/2 tsp baking powder, and 1/2 tsp salt. Stir with a large spoon or spatula until everything looks evenly combined, with no clumps of baking powder. This helps the leavening and spices distribute evenly through the casserole.

Step 3: Whisk together the wet ingredients

In a separate medium bowl or large measuring jug, whisk together the 2 1/2 cups milk, 1 cup mashed bananas, and 2 eggs until smooth. Add the 1/2 cup peanut butter, 1/3 cup maple syrup or honey, 2 tsp vanilla, and 3 tbsp melted butter or coconut oil. Whisk again until the mixture is mostly smooth and the peanut butter is evenly incorporated. A few tiny specks of peanut butter are fine as long as there are no big chunks.

Step 4: Combine and thicken the batter

Pour the wet mixture into the bowl with the dry ingredients. Stir gently but thoroughly, scraping the bottom and sides of the bowl, until all the oats are moistened and there are no dry pockets. The mixture will look loose and quite liquid at this stage.

Let the batter sit on the counter for 5 minutes. This short rest gives the oats time to start absorbing the liquid so the finished baked oatmeal is custardy but not watery.

Step 5: Transfer to the pan and add the toppings

Give the batter one last stir, then pour it into your prepared 9×13-inch baking dish. Use a spatula to spread it into an even layer, making sure oats and peanuts are distributed throughout the pan.

Arrange the sliced banana over the top in rows or a scattered pattern. Sprinkle over the remaining 2–3 tbsp chopped peanuts.

In a small bowl or mug, gently warm the 2 tbsp peanut butter in the microwave for about 15–20 seconds until just runny, then drizzle it over the top of the casserole in thin ribbons. This creates a pretty marbled look and adds rich peanut flavor to every bite.

Step 6: Bake until set and golden

Place the dish in the preheated oven and bake for 30–35 minutes. The baked oatmeal is done when the edges are lightly browned, the top looks set and no longer shiny, and the center barely jiggles when you gently shake the pan. A toothpick inserted near the center should come out mostly clean, with a few moist crumbs but no wet batter.

If your oven runs cool and the center still looks very wet at 30 minutes, continue baking in 3–5 minute increments, checking frequently.

Step 7: Cool slightly, slice, and serve

Remove the dish from the oven and set it on a cooling rack. Let it stand for at least 10 minutes. This brief rest helps the oatmeal firm up so you can cut neat squares.

Cut into 10 servings. Serve warm, optionally with a drizzle of maple syrup, a sprinkle of extra cinnamon, and/or a splash of milk or spoonful of yogurt over the top for added creaminess. This casserole is delicious warm from the oven, at room temperature, or gently reheated the next day.

Pro Tips

• Use very ripe bananas: Bananas with plenty of brown spots are sweeter and mash more easily, adding natural sweetness and moisture.
• Stir natural peanut butter well: If using natural peanut butter, make sure it is thoroughly stirred so the oil is incorporated; otherwise, the batter can separate.
• Adjust sweetness to taste: If your bananas are extra sweet, you can reduce the maple syrup/honey to 1/4 cup. For a more dessert-like casserole, increase to 1/2 cup.
• Do not overbake: Pull the casserole when the center is just set. Overbaking will make the texture dry instead of custardy and tender.
• For dairy-free: Use non-dairy milk (such as almond or oat milk) and swap the butter for coconut oil or a neutral vegetable oil.

Variations

• Chocolate Chip Peanut Butter Banana: Fold 1/2–3/4 cup dark or semi-sweet chocolate chips into the batter before baking. Sprinkle a few extra on top for a bakery-style look.
• Berry Peanut Butter Oat Bake: Gently fold 1 cup fresh or frozen berries (blueberries or raspberries work well) into the batter. Add a few berries on top around the banana slices.
• Crunchy Streusel Topping: Mix 1/3 cup oats, 2 tbsp brown sugar, 2 tbsp chopped peanuts, and 2 tbsp melted butter. Crumble over the top before baking for a sweet, crunchy crust.

Storage & Make-Ahead

Let the baked oatmeal cool completely, then cover the dish tightly with foil or transfer individual squares to airtight containers. Store in the refrigerator for up to 4–5 days.

To reheat a single serving, microwave on high for 45–60 seconds until warmed through, adding a splash of milk if you like it softer. To reheat a larger portion or the whole pan, cover with foil and warm in a 325°F (165°C) oven for about 15–20 minutes.

For longer storage, cut the cooled oatmeal into squares, wrap each piece tightly in plastic wrap or parchment, and place in a freezer bag. Freeze for up to 2–3 months. Reheat from frozen in the microwave (1–2 minutes) or thaw overnight in the fridge before reheating.

Nutrition (per serving)

Approximate values for 1 of 10 servings, using 2% milk and maple syrup: about 380 calories, 14 g fat, 45 g carbohydrates, 6 g fiber, 16 g sugar, and 11 g protein. These numbers are estimates and will vary based on the specific brands and exact ingredients you use.