Preheat your oven to 350 F. Grease two 8-inch round cake pans and line the bottoms with parchment paper.
Whisk together the almond flour, gluten free flour, baking powder, baking soda, cinnamon, and salt in a medium bowl.
In a large bowl, combine the mashed bananas, brown sugar, eggs, oil, sour cream, and vanilla. Whisk until smooth. Pour the dry ingredients into the wet and stir until just combined with no streaks of flour remaining.
Divide the batter evenly between the prepared pans. Bake for 28 to 33 minutes until the cakes are golden brown and a toothpick inserted in the center comes out clean. Cool in the pans for 10 minutes, then turn out onto wire racks to cool completely.
Make the frosting by beating the softened butter on high speed for 3 minutes until very pale and creamy. Add the dulce de leche and beat until combined. Gradually add the powdered sugar on low speed, then add the cream and salt. Beat on high for 2 to 3 minutes until light and fluffy.
Place one cake layer on your serving plate and spread a thick layer of frosting over the top. Place the second layer on top. Frost the top and sides of the entire cake with the remaining frosting, using an offset spatula to create smooth sides.
Drizzle extra dulce de leche over the top of the cake, letting it drip down the sides. Garnish with a few banana slices. Refrigerate for 30 minutes to set before slicing.