Adjust oven rack to middle position and heat oven to 350ºF. Line a 12-cup muffin tin with foil liners and set aside.

In a large bowl, whisk together the allulose, sour cream, oil, eggs, color, vanilla, and salt until smooth. Add the almond flour, coconut flour, lupin flour, cocoa powder, psyllium, baking powder, xanthan gum, and baking soda and stir until evenly combined and smooth.

Using a large spoon, divide batter evenly between the muffin tins. Bake at 350ºF, rotating halfway through for 20-25 minutes, or until a toothpick inserted comes out clean. Let cool in the tin until cool enough to handle and then remove to a wire rack to cool completely.

Combine frosting ingredients in a large bowl and using a mixer, beat until smooth, light, and fluffy, about 5-7 minutes. Start slow and once everything is incorporated, increase the whipping speed.

Transfer to a piping bag and pipe onto cupcakes, or spread onto tops using a knife. Frost just before serving.