1/2 cup (1 stick/113 grams) unsalted butter, at room temperature, plus more for pan
1 cup (200 grams) granulated sugar
2 large eggs, at room temperature
1 1/2 cups (188 grams) all-purpose flour
1 teaspoon baking soda
1 teaspoon kosher salt
1 cup mashed very ripe bananas (3 medium bananas)
1/2 cup (113 grams) sour cream
1 teaspoon vanilla extract
1 1/2 teaspoons bourbon or dark rum
1/2 cup cranberries (fresh or frozen; if frozen, no need to defrost)
1 small ripe banana, peeled and halved lengthwise (optional)
Demerara sugar, for sprinkling (optional)

Preheat the oven to 350°F. Grease a 9-by-5-by-3-inch loaf pan; set aside. In a large bowl, using a handheld electric mixer, or using the bowl of a stand mixer, which has been fitted with the paddle attachment, beat the butter and granulated sugar on medium-high speed until light and fluffy, about 2 minutes. Add the eggs, and beat to incorporate.

In a medium bowl, whisk together flour, baking soda, and salt. Add to the butter mixture, and mix on low speed until just combined. Add the mashed bananas, sour cream, bourbon or rum, and vanilla, and mix on low just to combine. Stir in the cranberries and pour into prepared pan; smooth out the top with an offset spatula, if you like. Add the halved banana on top, if using, and sprinkle with the demerara sugar, if using.

Bake until a cake tester inserted into the center of the cake comes out clean, about 1 hour 10 minutes. Let rest in pan for 10 minutes, then run a butter knife around the perimeter of the bread and turn out onto a rack to cool.

The bread tastes better if you let it sit overnight, uncovered, to dry up a little bit and let the flavors meld.