First, preheat the oven to 350° F and line two cupcake pans with paper cupcake liners. Then, in a large bowl, mash the five large bananas using a fork or other mashing implement (the flavor and texture is much better if you use fresh bananas, not overripe/brown bananas – they should still be entirely yellow/yellow-green). Then, add in the melted butter, sugar, sour cream, eggs, and vanilla and stir together with the banana mash until fully combined. Add in the flour, almond meal/flour, baking powder, salt, and nutmeg and stir until fully combined again. Lastly, add in the chocolate chips (optional) and stir. Spoon the batter into the lined cupcake pans (each cup should each be 3/4 full). Bake for 20-24 minutes or until a skewer inserted into the center of a cupcake comes out clean. Let cool completely before frosting.
While the cupcakes are cooling, make the buttercream. First, blitz up a bag of freeze dried bananas in a food processor or nutribullet until it's a fine powder. Pour into a large bowl. Then, blend your yellow (not brown) banana in the blender or food processor until entirely pureed. Dump into the same bowl and then add in the salted room temp butter. Beat with an electric mixer until blended. Add in the powdered sugar, one cup at a time, until smooth. Add in yellow food coloring (optional) to your taste. If the buttercream is too thin, add more powdered sugar, if it's too stiff, add more pureed banana. Then, scoop into a piping bag and pipe onto cooled cupcakes. Add mini chocolate chips for decoration (optional) and then serve!