Preheat oven to 350 degrees F.

In a small saucepan melt 4 tablespoons of butter and divide between four 1-cup ramekins. Evenly sprinkle brown sugar and nuts over the butter in each ramekin. Arrange banana slices over the nuts, overlapping to fit.

In a bowl whisk together the flour, baking powder, cinnamon, and salt. In a separate bowl cream together the remaining butter and the granulated sugar. Beat in the eggs, one at a time, and then mix in vanilla. Stir in the dry ingredients, mixing until batter is just combined. Divide batter evenly among the four ramekins. Transfer the ramekins to a baking sheet and bake for 25 minutes, or until puffed and golden brown. Cool the ramekins on a rack for 5 minutes. Run a sharp knife around edges of ramekins and carefully invert onto serving plates.