Prep the pan: Line a 12-cup muffin tin with paper liners. Lightly mist with oil to prevent sticking.
Preheat the oven to 350°F (175°C).
Mix dry ingredients: In a large bowl, whisk almond flour, cocoa powder, coconut flour, baking powder, baking soda, salt, and sweetener until no lumps remain. If using espresso powder, add it here.
Whisk wet ingredients: In a separate bowl, whisk eggs, almond milk, melted butter, yogurt, and vanilla. If using liquid stevia, add it now.
Combine gently: Pour the wet mixture into the dry ingredients.
Stir with a spatula until just combined. The batter will be thick; that’s normal.
Fold in chips: Gently fold in the sugar-free chocolate chips. Don’t overmix or the muffins may become dense.
Fill the cups: Divide the batter evenly among the 12 liners, filling each about 3/4 full.
Sprinkle a few extra chips on top for a bakery look.
Bake: Place the pan in the center of the oven and bake for 16–20 minutes. They’re done when the tops spring back lightly and a toothpick comes out with a few moist crumbs.
Cool: Let muffins cool in the pan for 5 minutes, then transfer to a rack to cool completely. This helps them set and keeps the texture tender.