2 tbsp melted butter (for the swirl)
In a small bowl, combine 2 tbsp of melted butter, 1 tbsp of cinnamon, and 2 tbsp of sweetener. Stir until smooth. Set aside.
In a large mixing bowl, combine almond flour, protein powder, baking powder, and a pinch of salt. Stir until evenly distributed.
In another bowl, whisk together eggs, heavy cream, melted butter, and sweetener. Mix until smooth.
Add the wet ingredients to the dry ingredients and stir until just combined.
Scoop the muffin batter into the muffin tin, filling each cup about 2/3 full.
Drop a spoonful of the cinnamon swirl mixture into the center of each muffin.
Use a toothpick or skewer to swirl the cinnamon mixture through the batter.
Bake for 20-25 minutes, or until a toothpick inserted into the center comes out clean.
Let the muffins cool in the tin for 5 minutes before transferring them to a cooling rack to cool completely.