1
extra-large, extra-ripe banana, mashed (1/2 cup)
1/3 cup
heavy cream, plus more for brushing
1
large egg, lightly beaten
1 teaspoon
pure vanilla extract
2 cups
all-purpose flour
1/3 cup
packed dark brown sugar
2 1/2 teaspoons
baking powder
1/2 teaspoon
kosher salt
1/2 cup
(1 stick) cold unsalted butter, cut into roughly 1/2-inch pieces
2 1/4 ounces
semisweet chocolate, chopped (1/2 cup)
1 1/4 ounces
hazelnuts, toasted, skinned, and finely chopped (about 1/4 cup)