Preheat the oven to 350°F (180°C). Grease and flour two 8-inch (20 cm) cake pans.
Prepare the crumb topping: In a bowl, mix brown sugar, flour, and chopped pecans. Stir in melted butter until crumbly. Set aside.
For the cake: In a large bowl, sift together flour, baking powder, baking soda, and salt.
In another large bowl, cream together butter and sugar until light and fluffy. Add eggs one at a time, beating well after each addition.
In a medium bowl, mix mashed bananas, vanilla, and yogurt.
Alternately add the flour mixture and banana mixture to the butter mixture, beginning and ending with the flour mixture.
Divide the batter evenly between the two prepared pans. Sprinkle each cake with half of the crumb topping.
Bake for 25-30 minutes or until a toothpick inserted in the center comes out clean. Cool in pans for 10 minutes, then remove to a wire rack to cool completely.
Once cooled, spread a thin layer of buttercream frosting on top of the first cake layer. Place the second cake layer on top.
Generously drizzle the top of the cake with caramel sauce. Decorate with extra pecans if desired.