Heat the oven to 325°. Line a 5- by 9-inch loaf pan, preferably one with a light interior, with enough waxed paper to drape over the long sides. This will make the baked bread a cinch to remove and the pan easy to clean. Set the pan aside.
Sift together the flour, baking powder, baking soda, and salt into a medium bowl. In a large bowl, cream the butter using an electric mixer. Gradually add the sugar, scraping down the sides of the bowl as necessary. Add the eggs one at a time, beating well after each addition. Next, add the vanilla extract and blend briefly. Set both bowls aside.
Peel the bananas and place them in a separate bowl. Mash them with a fork or a potato masher and measure out 1 cup. Add the sour cream and stir to blend. Set the bowl aside.
Using a wooden spoon, blend a third of the dry mixture into the butter-sugar mixture. Add the rest of the ingredients in this order, stirring well after each addition: half of the banana mixture, half of the remaining dry mixture, the rest of the banana mixture, the rest of the dry mixture. Next, add mix-ins if desired (see below).
5. Scrape the batter into the prepared pan and smooth the top with a spoon. Bake on the center oven rack until a tester inserted deep into the center of the bread comes out clean, about 70 to 75 minutes.
Transfer the bread to a cooling rack and cool it in the pan for about 20 minutes. Using the waxed paper, lift the bread from the pan and place it on the rack. Pull down the sides of the paper and allow the bread to cool thoroughly before slicing. Makes 10 or more servings.
For custom flavors that are sure to please everyone in your clan, try these fun variations.
Chocolate Chip Walnut Banana Bread: Follow steps 1 through 4, then stir 2/3 cup mini chocolate chips and 1/3 cup chopped walnuts into the batter.
Cranberry Banana Bread: Follow steps 1 through 4, then stir 1 cup dried cranberries into the batter.