Preheat oven to 350 degrees. Butter a 6-by-2-inch round cake pan. Line bottom with parchment paper; butter, and dust with flour. Set aside. Into a bowl, sift flour, baking soda, baking powder, salt, cinnamon, and cloves. In another bowl, whisk banana, buttermilk, and vanilla.

In a large bowl, cream butter and brown sugar until light and fluffy. Beat in egg. Add flour mixture in two batches, alternating with banana mixture. Stir in pecans. Pour into pan; bake until golden brown, about 45 minutes. Let cool 10 minutes. Run a knife around edge; invert onto a wire rack. Reinvert cake; let cool. Dust with confectioners' sugar, and serve with whipped cream if desired.