Add the egg whites to a bowl, whip them to stiff peaks and set aside.
In a separate bowl, add the almond flour, cocoa powder, salt, oat fiber, and baking powder. Whisk together and set aside.
In another bowl, whisk together, the egg yolks and swerve confectioners. Add in the heavy cream, sour cream, vanilla and coffee extracts and whisk. Mix in the dry ingredients until combined.
Fold in the egg whites, careful not to deflate them.
Scoop the batter into silicone cupcake liners or a greased muffin pan. Bake for 15-18 minutes or until a toothpick, when inserted, comes out clean. Allow to cool completely before frosting.
To Make the Frosting
Whip the mascarpone and butter together in a bowl using a hand mixer. Add most of the heavy cream (reserving about a tablespoon), swerve confectioners (or powdered erythritol), peanut butter and vanilla extract, then mix until smooth and creamy.
Add more of the heavy cream if needed, to get your desired consistency. Add the frosting to a piping bag fitted with the tip of your choice (ziplock bag with the tip cut off will work too), and chill in the fridge until the cupcakes have cooled completely. Frost the cupcakes and finish with a dusting of unsweetened cocoa powder.
The Oat Fiber is really important in this recipe. I use it in so many recipes, because of the amazing texture it gives whatever I am baking! It is hands down, the best ingredient I've baked with and is really worth buying. I use Lifesource Foods Oat Fiber 500 and I buy it in the 16 ounce bag on Amazon (link in recipe). The bag lasts a while because you don't need to use much in your recipes.Oat Fiber, is not the same as Oat Flour, which is made from grinding oats. Oat Fiber is made from grinding the outside husks of oats and is pure insoluble fiber. Insoluble fibers do not dissolve in water and are not broken down in the digestive tract.