Preheat the oven to 350°F. Line 6 muffin pan cavities with foil liners and lightly grease the liners.
In a large bowl, whisk the eggs, oil, vanilla, and stevia.
Add the almond flour and whisk it in thoroughly until the batter is smooth. Whisk in the salt and baking powder.
Divide the batter between the cupcake liners. The batter will be fairly thin.
Bake the cupcakes until puffed and a toothpick inserted in their center comes out clean, 15-17 minutes.
Place the pan on a cooling rack for 5 minutes, then remove the cupcakes from the liners and place them directly on the cooling rack. Cool them completely for about an hour, or place them in the fridge for 20 minutes to cool them quickly.
If your cupcakes have uneven domes, gently shave them off with a paring knife before frosting.
To make the frosting, place the softened unsalted butter, heavy cream, cocoa powder, vanilla, and stevia in a medium bowl. Using a handheld electric mixer, beat on low to incorporate, then beat on medium for about 1 minute until the frosting is light and fluffy.
Spoon the frosting on top of the cupcakes and gently spread it. Or use a piping bag to pipe it onto the cupcakes.
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Notes
I highly recommend using greased foil liners when baking with almond or coconut flour. It's been my experience that these baked goods do much better in terms of sticking when I use foil liners.
Dutch-processed cocoa powder is not as acidic as natural cocoa powder. It's smoother, milder, and darker. So, it works best in this recipe. Dutch-processed cocoa powder will usually be marked as "processed with alkali."
A granulated sweetener in the frosting will feel grainy, so please use a powdered sweetener. Add 1-2 extra tablespoons of heavy cream if the frosting is too thick.
Once completely cool, store these cupcakes in an airtight container in the fridge for up to 5 days. Remove them from the fridge an hour before enjoying them. The frosting is best at room temperature. You can freeze these cupcakes for up to three months.