Preheat the oven to 350°F.
Line a standard muffin pan with 12 cupcake liners.
In a medium bowl, whisk together the almond flour, coconut flour, baking powder, and salt.
In a large bowl, beat the softened butter and granulated sweetener for approximately three minutes.
Add the eggs one at a time, mixing after each addition.
Add the sour cream, vanilla extract, and optional butter extract.
Gradually mix in the dry ingredients just until combined.
Let the batter rest for approximately three minutes.
Divide the batter evenly among the cupcake liners.
Bake for 18 to 22 minutes, until the tops are set and a toothpick comes out clean or with a few moist crumbs.
Cool in the pan for approximately 10 minutes.
Transfer the cupcakes to a cooling rack and cool completely.
To make the frosting, beat the softened butter and cream cheese until smooth.
Gradually add the powdered sweetener.
Add the vanilla, salt, and one tablespoon of heavy cream.
Beat for three to five minutes, adding the remaining cream only if needed.
Pipe or spread the frosting over the cooled cupcakes.
Add optional decorations and refrigerate until ready to serve.
