Very lightly adapted from Super Natural Every Day. Heidi Swanson recommends blueberries or huckleberries or a mix. I've had good luck with just about every sort of berry; I've also used frozen, without incident. And for the record, I've added slightly more nuts here, for extra crunch. —Nicholas Day
walnuts, toasted and chopped
1 1/2 teaspoons
unsalted butter, melted and cooled slightly
Preheat the oven to 375 degrees. Butter the inside of a square 8-inch baking dish.
In a bowl, combine the oats, half of the walnuts, the baking powder, cinnamon, and salt.
In another bowl, whisk together the maple syrup, the milk, egg, half of the butter, and the vanilla.
Spread a single layer of bananas across the bottom of the buttered baking dish. Sprinkle about two-thirds of the berries on top. Cover all that with the oat mixture and then drizzle the milk mixture over the oats. Scatter the remaining berries and walnuts over the top.
Bake for 35 to 45 minutes, until the top is golden and the oats are set. Let cool for a few minutes. Drizzle with the remaining melted butter and serve.