The key to delicious and moist pound cake is making sure you have extremely ripe bananas — nice and dirty-brown. Ideally, I buy bananas aheads of time and store them in a brown bag in a drawer; do not refrigerate. Helpful hint: If you are in a pinch, I suggest begging a produce department employee to find some ripe bananas in the back (they usually pull the bananas that look too ripe and throw them away).
Adapted from "Sweetness: Delicious Baked Treats For Every Occasion" by Sarah Levy.
Preheat the oven to 350 degrees.
Mix handful of flour into the chocolate chips to coat them (this ensures that the chocolate chips don't all end up at the bottom of the loaf). Sift together the flour, baking powder, baking soda, and salt. Combine the sour cream and mascarpone in a bowl with a spatula.
In the bowl of a stand mixer fitted with the paddle attachment, or in a mixing bowl (if using a hand mixer), cream together the butter and cinnamon on high speed. Gradually add the sugar, about 1 tablespoon at a time. Continue to beat until the mixture is light in color and fluffy in texture.
Stop the mixer and scrape down the sides of the bowl. Then, turn the mixer back on to medium speed and add in the egg. Add 1/3 of the flour mixture to the mixing bowl, beating just until incorporated. Add 1/3 of the sour cream-mascarpone mixture to the mixing bowl until it is just barely incorporated. Alternate adding in the rest of the flour and sour cream-mascarpone mixtures to the mixing bowl.
Turn off the mixer. Using a spatula, fold in the pureéd bananas and the miniature chocolate chips. Do not overmix.
Prepare a 9-by-5-by-3-inch loaf pan by coating it entirely with softened butter using a pastry brush. Then, pour a handful of flour into the pan. Bake at 350 degrees for 50 minutes or until a toothpick inserted into the center of the pound cake comes out clean.