Preheat oven to 350 degrees. Grease a 9×5″ loaf baking pan and sprinkle with granulated sugar. Combine banana, sour cream and vanilla in a mixing bowl. In another bowl, sift together flour, baking powder, baking soda, salt and cinnamon.

In another large bowl, beat the butter and brown sugar with an electric mixer on medium speed until light and fluffy, about 3 & 1/2 minutes. Add eggs one at a time and beat on medium speed until fully combined, about 1 minute each. Add banana mixture and beat until just combined, about 30 seconds. Add dry ingredients in 2 batches, beating on low after each addition and scraping down the sides of the bowl if necessary until fully incorporated, about 20 seconds per batch. Fold in the walnuts and raisins. Transfer batter to prepared baking pan and smooth the top with a spatula.

Bake, rotating halfway through, until batter is set, top is dark golden brown and starting to crack, sides are starting to pull away from pan and a toothpick inserted into the center of bread comes out clean, 65-75 minutes.

Cool in pan on a wire rack for 20-30 minutes. Run a butter knife around the perimeter of pan to loosen the loaf. Then tap gently on its side until the loaf releases. Transfer to cutting board and let cool for an hour or overnight before slicing.