Overnight Baked Oatmeal Casserole

Prep Time: 10 minutes | Cook Time: 40 minutes | Chill Time: overnight | Total Time: 8 hours 50 minutes | Servings: 9

Most baked oatmeal recipes tell you to let it sit for 30 minutes before baking. That’s not long enough. The oats need at least 8 hours to fully absorb the liquid, otherwise you get crunchy oat pockets floating in egg custard. This version sits overnight, which means you mix it before bed and wake up to something that actually tastes cohesive.

What Makes It Work

The overnight soak is non-negotiable. Oats are slow to hydrate. Give them time and they turn soft and creamy. Rush it and they stay grainy.

Greek yogurt adds protein without making it taste like a protein shake. One cup gives you an extra 20 grams of protein for the whole batch.

Mashed banana replaces half the sweetener. Two bananas give you natural sugar and help everything bind together. You can taste the banana, but it’s not banana bread.

The baking powder makes it rise slightly instead of sitting dense and heavy. It’s the difference between cake-like and porridge-like.

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Ingredient Notes

Oats: Old-fashioned rolled oats only. Not instant (turns to mush), not steel-cut (stays too chewy). The flat rolled oats absorb liquid evenly.

Greek yogurt: Full-fat or 2%. Nonfat doesn’t add enough richness. Plain only, flavored yogurt has too much sugar.

Bananas: Use ripe ones with brown spots. They mash easier and taste sweeter. Unripe bananas don’t break down well.

Mix-ins: One cup total. Berries, nuts, chocolate chips, dried fruit, coconut. Whatever you want. Frozen berries work but reduce milk by 1/4 cup because they release water.

Sweetener: Quarter cup honey or maple syrup. Adjust based on how sweet your mix-ins are. If you’re adding chocolate chips, you might want less.

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Instructions

Whisk together milk, eggs, Greek yogurt, mashed bananas, honey, vanilla, and salt in a large bowl. The banana doesn’t need to be perfectly smooth.

Add oats, baking powder, and cinnamon. Stir until combined. The mixture looks very wet, almost soup-like. That’s correct.

Fold in your mix-ins. Save a handful for the top if you want them visible.

Grease a 9×13-inch dish, pour in the mixture, spread it even. Cover tight. Refrigerate 8-24 hours.

Next morning: heat oven to 350°F. Pull the dish out, let it sit while the oven heats. Remove the cover, sprinkle on reserved mix-ins if you saved them.

Bake 35-40 minutes until the center doesn’t jiggle, edges are golden, top has a slight crust. It puffs while baking and settles as it cools.

Wait 10 minutes before cutting.

Swapping Things Out

Different fruit works: blueberries and lemon zest, diced apples with extra cinnamon, strawberries and almonds, peaches and pecans.

For chocolate: add 1/4 cup cocoa powder and chocolate chips.

For pumpkin: replace bananas with 1 cup pumpkin puree, add pumpkin pie spice.

For peanut butter: add 1/3 cup peanut butter to the wet ingredients.

Higher protein: add 1/4 cup vanilla protein powder with the dry ingredients, or replace half the milk with more Greek yogurt.

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What to Serve It With

This is sweet enough to stand alone. Fresh berries on top, a dollop of yogurt, maple syrup, sliced banana, or nut butter all work. Coffee or tea.

More Breakfast Recipes:

Greek Yogurt Protein Casserole (26g Protein)

Low Calorie Veggie Breakfast Bake (165 Calories)

Sweet French Toast Casserole