Preheat and prep: Heat the oven to 375°F (190°C).
Grease an 8x8-inch baking dish or a similar 2-quart dish with butter or oil.
Mix dry ingredients: In a large bowl, combine oats, sliced almonds, baking powder, cinnamon, and salt. Stir to distribute everything evenly.
Whisk wet ingredients: In a separate bowl or measuring cup, whisk the eggs, milk, maple syrup, melted coconut oil or butter, and vanilla until smooth.
Combine: Pour the wet mixture into the dry ingredients and stir until the oats are fully moistened. The mixture will look loose—this is right.
Add blueberries: Gently fold in the blueberries.
If using frozen berries, scatter them in straight from the freezer to avoid purple streaks.
Assemble: Pour the mixture into the prepared dish. Smooth the top. Sprinkle a handful of extra sliced almonds over the surface for crunch.
Bake: Bake for 35–40 minutes, until the center is set and the top is lightly golden.
The edges should look slightly toasted.
Rest: Let it cool for 10–15 minutes. This helps it set so you can slice clean squares.
Serve: Enjoy warm as is, or top with a spoonful of yogurt, a drizzle of maple syrup, and extra blueberries.