Preheat the oven to 350 F (177 C). Lightly grease a 15 x 10 pan (or 9 x 13). In a bowl, melt the butter and allow to cool until warm to the touch. In a mixing bowl, whisk the flour, baking soda, ground cinnamon and salt together until well combined.
2 cups (240 g) all purpose flour, 1 teaspoon ground cinnamon , ¾ teaspoon baking soda, ½ teaspoon salt
Whisk the bananas until smooth with just a few lumps. Whisk in the, melted butter, sugar, eggs, sour cream and vanilla extract together until smooth and well combined.
1¼ cups mashed bananas , ½ cup (113 g) unsalted butter, melted and cooled to warm, 1¾ cups (350 g) granulated sugar, 2 large eggs (US), room temperature, 1 cup (240 g) sour cream, room temperature, 2 teaspoons (10 ml) vanilla extract
Whisk the dry ingredients into the wet well combined with no visible pieces of flour.Pour the banana bar batter into the prepared pan. Use a flexible spatula to smooth the batter evenly across the pan. Bake for about 20 - 25 minutes or until the banana cake bounces back with gently pressed. The edges of the banana bread bars will also pull slightly away from the pan.
Cool the bars in the pan to room temperature. Cool completely before frosting with the cream cheese icing.
Make the cream cheese frosting for banana bars by beating the butter and cream cheese together until fluffy and well combined. Pour in the vanilla extract, powdered sugar and 1 teaspoon (5 ml) milk. Beat the cream cheese frosting until smooth and well combined.
8 oz. (226 g) cream cheese, room temperature, ½ cup (113 g) unsalted butter, room temperature, 2 teaspoons (10 ml) vanilla extract , ¼ teaspoon salt, 3½ cups (420 g) powdered sugar, 1 tablespoons (15 ml) milk, as needed
Spread the cream cheese frosting on top of the fully cooled banana sheet cake bars. If the frosting is too warm or soft, place the frosted banana bars in the fridge for 20-30 minutes. Slice and enjoy!