Mix together the oats, half of the walnuts, sugar, baking powder, cinnamon, and salt. Set aside.

In another bowl, whisk together the milk, egg, butter, and vanilla.

Generously butter the bottom of an 8-inch pan and add sliced bananas and half of the blackberries.

Add the oat mixture to the top of the fruit.

Pour the milk mixture over the oats. Use a spoon to make sure the milk mixture is incorporated throughout the oats.

Add the remaining walnuts and blackberries.

Bake in a preheated 375 degree oven with the rack in the top third of the oven for 35 to 45 minutes. The top should be golden and the oatmeal should be set.

Let the oatmeal cool for a few minutes and serve with maple syrup and if you are really feeling wild, more melted butter.