Preheat your oven to 350 degrees F. Coat a loaf pan with non-stick cooking spray and set aside.
In a medium mixing bowl, combine 2 cups all-purpose flour, 1 teaspoon baking soda, 1 teaspoon baking powder, and 1/4 teaspoon salt. Set aside.
In a large mixing bowl, beat together 1/2 cup unsalted butter, 1/2 cup light brown sugarand 1/4 cup granulated sugar until fluffy, about 1 minute. Add 1/4 cup sour cream, 2 large eggs, 2 tablespoons milk, and 1 teaspoon vanilla extract. Mix until smooth, scraping the side of the bowl as needed.
Add half of the dry ingredients to the wet ingredients and mix until just combined. Add the other half and mix again. Add 3 very ripe bananas and mix until combined.
Pour the batter into the prepared loaf pan and use a spatula to spread it into an even layer.
Bake for 50 to 70 minutes, or until a toothpick inserted in the center comes out clean.
Here's my go-to trick: Set the loaf pan on the middle rack with a baking sheet on the rack underneath. It keeps the bottom from browning too fast while the rest of the loaf catches up.
Remove from the oven and place on a wire rack until cool enough to handle. Cut into slices and serve warm or at room temperature.
Notes
Nutritional information is based on 1 loaf cut into 8 slices.
If you like nuts in your banana bread, stir in ½ to 1 cup of chopped walnuts or pecans before pouring the batter into the loaf pan.
Don't worry if the batter looks curdled after adding the sour cream and milk. It smooths out once the dry ingredients are incorporated.
In a hurry to ripen your bananas? Microwave them unpeeled in 30-second intervals until the skins turn black and the fruit is soft. Let them cool before using.