1-Getting started: Getting started with these banana bread bars is straightforward and fun, beginning with preheating your oven to 350°F (175°C). Grease an 11×15-inch jelly roll pan to prevent sticking, then brown a total of 1 1/4 cups unsalted butter over medium heat until it turns a light amber color for that rich flavor. Reserve 1/2 cup of the browned butter for the batter, and set the rest aside for the frosting by adding 2 tablespoons of extra butter and refrigerating it to solidify.

2-Next, in a mixing bowl, combine the reserved 1/2 cup browned butter with 1 cup granulated sugar and 1/2 cup packed light brown sugar, whisking until smooth. Add 2 large eggs, 1 cup sour cream, 1 1/2 cups mashed ripe banana, and 1 teaspoon vanilla extract, mixing everything together thoroughly. For more tips on managing ingredients like flour, stir in 1 teaspoon baking soda, 1/2 teaspoon kosher salt, and 2 cups all-purpose flour just until combined be sure not to overmix to keep the bars tender, as mentioned in our guide on baking tips for beginners.

3-Pour the batter into your prepared pan and smooth it out. Bake for 25-30 minutes, or until a toothpick comes out clean. While the bars cool slightly, whip the chilled browned butter with 3 cups powdered sugar, 1 teaspoon vanilla extract, and 1/4 cup milk at room temperature until smooth for the frosting. Spread it over the warm bars, then let everything cool for 30 minutes before slicing into 24 pieces. This step ensures the bars stay moist and flavorful, with tips like measuring bananas by volume for accuracy and incorporating all those browned butter bits.