Preheat your oven to 350°F. Line 12 muffin cups with foil (not paper) liners and grease the liners.
In a large bowl, whisk the eggs. One by one, whisk in the butter, stevia, vanilla, and milk.
Whisk in the coconut flour, then the cocoa powder. Finally, whisk in the kosher salt and baking soda.
Using a 4-tablespoon scoop, divide the batter evenly among the prepared muffin cups.
Bake the muffins until they are set and a toothpick inserted in their center comes out clean, 18-20 minutes.
Cool the muffins for 10 minutes in the pan on a cooling rack, then cool them directly on the cooling rack until completely cool, about 30 more minutes. The muffins taste much better when they've had a chance to cool and set.
Video
Notes
Occasionally, baking soda can cause a reaction in baked goods that results in an ammonia smell. If you're concerned about it happening, use 4 teaspoons of fresh baking powder (gluten-free if needed) instead of baking soda.
Since coconut flour is so absorbent, it's best to measure it by weight and not by volume. Each additional tablespoon makes a big difference, so it's best to be as accurate as possible.
If using Dutch-processed cocoa powder, substitute 4 teaspoons of baking powder (gluten-free if needed) for the 1 teaspoon of baking soda.
You can use a granulated sweetener instead of stevia, increasing the amount of liquid you add to the batter if it's too dry. Add water or milk, a tablespoon at a time, until you reach a good consistency.
The leftovers keep well in an airtight container in the fridge for up to five days. Warm them briefly in the microwave before serving (after removing the foil liners, of course). You can also freeze these muffins in freezer bags for up to three months.