Quick Recipe Version (TL;DR)
Quick Ingredients
- 3 cups (240 g) old-fashioned rolled oats
- 1/2 cup (100 g) packed light brown sugar
- 2 teaspoons ground cinnamon
- 2 teaspoons baking powder
- 1/2 teaspoon fine salt
- 2 cups (480 ml) whole milk
- 2 large eggs
- 1/4 cup (57 g) unsalted butter, melted and slightly cooled, plus 1 teaspoon (5 g) for greasing
- 1 teaspoon vanilla extract
- 2 cups (260 g) cored apples, cut into 1/2-inch dice
- Optional for serving: cold milk, vanilla yogurt, or pure maple syrup
Do This
- 1. Heat the oven to 350°F (175°C). Grease a deep 9-inch square baking dish with 1 teaspoon butter.
- 2. Stir together the oats, brown sugar, cinnamon, baking powder, and salt.
- 3. In another bowl, whisk the milk, eggs, melted butter, and vanilla.
- 4. Combine the wet and dry mixtures, fold in the diced apples, and spread evenly in the dish.
- 5. Bake for 45 minutes, checking at 40 minutes, until the edges are golden and the center is set but tender.
- 6. Rest for 10 minutes, divide into 8 portions, and serve warm with cold milk, vanilla yogurt, or maple syrup.
Why You’ll Love This Recipe
- Cozy, familiar flavors: Apples, cinnamon, and brown sugar make the kitchen smell wonderful.
- A satisfying texture: The edges bake up golden while the middle stays moist, tender, and full of hearty oats.
- Simple pantry ingredients: No special equipment or hard-to-find ingredients are needed.
- Breakfast for several days: Make one casserole and reheat individual portions throughout the week.
Grocery List
- Produce: About 2 medium apples, such as Honeycrisp, Fuji, or Braeburn.
- Dairy: Whole milk, unsalted butter, and optional vanilla yogurt for serving.
- Pantry: Old-fashioned rolled oats, light brown sugar, ground cinnamon, baking powder, fine salt, vanilla extract, and optional pure maple syrup.
- Eggs: 2 large eggs.
Full Ingredients
Dry Ingredients
- 3 cups (240 g) old-fashioned rolled oats: Use rolled oats, not steel-cut oats or instant oatmeal.
- 1/2 cup (100 g) packed light brown sugar: Break up any firm lumps before mixing.
- 2 teaspoons ground cinnamon
- 2 teaspoons baking powder
- 1/2 teaspoon fine salt
Wet Ingredients
- 2 cups (480 ml) whole milk
- 2 large eggs
- 1/4 cup (57 g) unsalted butter, melted: Let it cool for 5 minutes so it is warm rather than hot.
- 1 teaspoon vanilla extract
Apples and Pan Preparation
- 2 cups (260 g) diced apples: Core and cut into 1/2-inch pieces; peel them for a softer texture or leave the skins on. You will need about 2 medium apples.
- 1 teaspoon (5 g) softened unsalted butter: For greasing the baking dish.
Optional Toppings
- Cold milk: 2 tablespoons (30 ml) per serving.
- Vanilla yogurt: 2 tablespoons (30 g) per serving.
- Pure maple syrup: 1 teaspoon (5 ml) per serving, or to taste.
Step-by-Step Instructions
Step 1: Heat the oven and prepare the dish
Set a rack in the middle of the oven and preheat to 350°F (175°C). Grease the bottom and sides of a deep 9-inch square baking dish with a capacity of at least 2 quarts using 1 teaspoon softened butter. Melt the remaining 1/4 cup butter and let it cool for 5 minutes while you prepare the other ingredients.
Core the apples and cut them into 1/2-inch dice. Measure 2 cups of diced apples. Peeling is optional: peeled apples blend more softly into the oatmeal, while unpeeled apples add a little texture and color.
Step 2: Mix the dry ingredients
In a large mixing bowl, stir together the oats, brown sugar, cinnamon, baking powder, and salt. Use the back of a spoon or your fingers to break up any brown sugar lumps. Mix thoroughly so the cinnamon and baking powder are evenly distributed.
Step 3: Whisk the wet ingredients
In a separate medium bowl, whisk the milk and eggs until the eggs are fully blended. Whisk in the slightly cooled melted butter and vanilla. The butter should be warm, not hot, so it does not cook the eggs.
If the milk is very cold, the butter may form small flecks as you whisk. That is fine; they will melt into the casserole in the oven.
Step 4: Combine and add the apples
Pour the milk mixture over the oat mixture and stir until every oat is moistened. Fold in the diced apples, making sure they are evenly distributed. The mixture will look loose and milky at this stage; the oats will absorb the liquid as they bake.
Transfer everything to the prepared baking dish, scraping in all the liquid. Spread the oats and apples into an even layer with a spoon or spatula. Bake promptly rather than letting the mixed batter sit for an extended time.
Step 5: Bake until golden and tender
Bake uncovered for 45 minutes, beginning to check at 40 minutes. The edges should be golden brown, the surface lightly browned, and the center set without a puddle of liquid or a loose wobble when you gently nudge the dish. A knife inserted near the center should come out moist but without uncooked egg mixture.
For an additional doneness check, the center should reach at least 160°F (71°C) on an instant-read thermometer. If the top is browning before the center is ready, loosely cover it with foil for the remainder of baking. Avoid baking until completely dry; the middle should remain tender.
Step 6: Rest and serve warm
Place the dish on a heatproof surface and let the oatmeal rest for 10 minutes. This gives the oats time to finish absorbing moisture and makes the casserole easier to portion. Divide into 8 servings; it should hold together gently while still feeling soft enough to scoop.
Serve warm in shallow bowls or on plates. Add 2 tablespoons cold milk around each portion, spoon 2 tablespoons vanilla yogurt on top, or finish with 1 teaspoon maple syrup. The contrast between warm cinnamon oatmeal and cold milk is especially comforting.
Pro Tips
- Choose apples that hold their shape: Honeycrisp, Fuji, and Braeburn give you tender pieces rather than disappearing into the oats.
- Keep the dice consistent: Small, 1/2-inch apple pieces cook more evenly than large chunks.
- Use the right oats: Steel-cut oats will not soften properly with these measurements and baking times. Instant oatmeal can turn mushy.
- Check the center, not just the edges: Golden edges can appear before the middle has finished cooking.
- Do not skip the rest: The casserole firms up as it stands, so portioning it immediately can make it seem wetter than it really is.
Variations
- Apple-walnut oatmeal: Fold in 1/2 cup (60 g) chopped walnuts with the apples for a little crunch.
- Apple-raisin oatmeal: Add 1/3 cup (50 g) raisins with the apples. Keep the remaining ingredients and baking instructions unchanged.
- Dairy-free version: Replace the milk with 2 cups (480 ml) unsweetened oat milk and the melted butter with 1/4 cup (60 ml) neutral oil. Grease the dish with 1 teaspoon oil and serve with dairy-free yogurt.
Storage & Make-Ahead
Refrigerate: Refrigerate leftovers within 2 hours of baking. Cover tightly or transfer portions to an airtight container and refrigerate for up to 4 days.
Reheat: Place one chilled serving in a microwave-safe bowl, add 1 tablespoon (15 ml) milk, and cover loosely. Microwave on high for 60 seconds, then continue in 20-second intervals until the center reaches 165°F (74°C). For several portions, place them in a baking dish, add 1 tablespoon milk per portion, cover with foil, and heat at 325°F (165°C) for 20–25 minutes, or until heated through to 165°F (74°C).
Freeze: Wrap cooled individual portions and place them in a freezer-safe container. Freeze for up to 2 months, thaw overnight in the refrigerator, and reheat as directed above.
Prepare ahead: Mix the dry ingredients and refrigerate the whisked wet ingredients separately up to 24 hours ahead. Prepare the apples just before baking, then combine everything and bake as directed. For the most consistent texture, avoid soaking the fully mixed oatmeal overnight.
Nutrition (per serving)
Calories: 295 kcal | Carbs: 41g | Protein: 9g | Fat: 12g | Saturated Fat: 6g | Fiber: 4g | Sugar: 19g | Sodium: 310mg | Cholesterol: 69mg
Nutrition is estimated for one-eighth of the casserole, including the butter used to grease the dish. Optional toppings and variations are not included.
