- 5 ounces (10 Tbsp.) unsalted butter, at room temperature, plus more for the pan
- 1¾ cups dark brown sugar, divided
- 2 teaspoons pure vanilla extract
- 2 eggs, at room temperature
- 1½ cups all-purpose flour
- 1 teaspoon baking powder
- ½ teaspoon fine salt
- ½ cup sour cream
- 4 very ripe large bananas, halved lengthwise
- Vanilla ice cream, for serving
- Preheat the oven to 375°F. Butter and line a 9-by-13-inch pan with parchment. Butter the parchment.
- Beat the butter and 1½ cups of the brown sugar with an electric mixer on medium-high until light and fluffy, 5 minutes. Scrape down the sides of the bowl and add the vanilla and eggs, one at a time. Beat to combine.
- Whisk together the flour, baking powder, and salt. Add to the batter, alternating with the sour cream, beginning and ending with the flour mixture. Beat until just combined.
- Spoon the batter into the prepared pan and smooth with a spatula. Lay the bananas, cut-side up, across the batter (they will sink in) and sprinkle with the remaining brown sugar. Bake until a toothpick inserted in the center of the cake (avoiding the bananas) comes out clean, 35 to 45 minutes. Serve warm with vanilla ice cream.