Step 1: Preparing the Berry Base In a medium bowl, gently toss the berries with the granulated sugar and lemon juice. Let them sit while you prepare the batter. This helps draw out their juices and creates that wonderful, syrupy compote as it bakes. If using frozen berries, don’t thaw them first—just toss them straight in.
Step 2: Mixing the Wet Ingredients In a large bowl, whisk together the eggs, milk, maple syrup, and melted butter until they are fully combined and slightly frothy. The melted butter should be cool enough that it doesn’t cook the eggs.
Step 3: Combining the Dry Ingredients In a separate small bowl, whisk together the rolled oats, flour, baking powder, cinnamon, and salt. This ensures the leavening is evenly distributed so the bake rises uniformly.
Step 4: Creating the Oat Batter Pour the dry ingredient mixture into the bowl of wet ingredients. Stir with a spatula or wooden spoon just until there are no dry streaks of flour left. Be careful not to overmix—a few small lumps are perfectly fine. The batter will be thick and a little lumpy.
Step 5: Assembling the Bake Preheat your oven to 375°F (190°C). Generously butter an 8×8-inch or similar 2-quart baking dish. Pour the macerated berry mixture (with all its juices) into the prepared dish and spread it into an even layer. Then, dollop the oat batter over the berries. It won’t cover them completely; that’s the goal. Use a spatula to gently spread it as best you can, leaving some berries peeking through.
Step 6: Baking to Golden Perfection Place the dish in the preheated oven and bake for 35-40 minutes, or until the top is golden brown, the edges are bubbling, and the center is set and springs back lightly when touched. A toothpick inserted into the center of the oat cake should come out clean. If the top is browning too quickly, loosely cover it with foil for the last 10 minutes.
Step 7: Cooling and Resting Remove the bake from the oven and let it rest in the dish on a wire rack for at least 10 minutes. This is a crucial step—it allows the juices to thicken and the structure to set, making it much easier to scoop out cleanly.