Step 1

Preheat oven to 350°. Lightly coat 8½x4½" loaf pan with nonstick spray and line with parchment paper, leaving a generous overhang on long sides. Whisk flour, baking soda, and salt in a medium bowl.

Step 2

Using an electric mixer on medium-high speed, beat brown sugar, mascarpone, and butter in a large bowl until light and fluffy, about 4 minutes. Add eggs one at a time, beating to blend after each addition and scraping down sides and bottom of bowl as needed.

Step 3

Reduce speed to low, add flour mixture, and mix until just combined. Add bananas and mix just until combined. Fold in chocolate and/or walnuts, if using. Scrape batter into prepared pan; smooth top.

Step 4

Bake bread until a tester inserted into the center comes out clean, 60–65 minutes. Transfer pan to a wire rack and let bread cool in pan 1 hour. Turn out bread and let cool completely (if you can resist) before slicing.