One layer of this banana cake and another layer of Coconut Cake surrounded by cream cheese frosting and colored coconut flakes comprise the very special Alexis' Heart Cake.
Preheat oven to 350 degrees. Butter a 10-inch heart-shaped cake pan; line bottom with parchment paper. Butter parchment and dust with flour, tapping out excess; set aside.
In a medium bowl, whisk together flour, baking powder, baking soda and salt. In a small bowl, stir together mashed banana, sour cream, and vanilla; set aside.
In the bowl of an electric mixer fitted with the paddle attachment, beat together butter and sugar on medium speed until light and fluffy, 3 to 4 minutes, scraping down the sides of the bowl, as needed. Add the eggs, one at a time, beating well after each addition. With the mixer on low speed, add the reserved banana mixture, beating until combined. Add the flour mixture in two parts, beating until combined after each, 2 to 3 minutes, being careful not to overmix
Pour batter into prepared pan. Bake, rotating pan halfway through, until cake is golden brown and a cake tester inserted into the center comes out clean, 30 to 35 minutes.
Transfer pan to a wire rack to cool for 20 minutes. Invert cake onto rack; peel off parchment paper. Reinvert cake and let cool completely, top side up.