Preheat oven to 350°F (175°C). Line a muffin tin with paper liners or lightly grease with oil spray.
Mix dry ingredients: In a medium bowl, whisk almond flour, cocoa powder, coconut flour, baking powder, baking soda, and salt.
Mix wet ingredients: In another bowl, whisk eggs, stevia, almond milk, olive oil, and vanilla until smooth.
Combine: Stir dry ingredients into wet until just combined. Batter will be slightly thick.
Optional: Fold in chocolate chips.
Fill muffin cups ¾ full.
Bake 18–22 minutes, until a toothpick comes out mostly clean.
Cool 5 minutes in the pan, then transfer to a wire rack.