Preheat oven to 350°F and generously spray a muffin tin with cooking spray.
In a large bowl, whisk together 3 cups almond flour (300 grams), 4 tablespoons coconut flour (firmly packed, 32 grams), 1 tablespoon baking powder, 1 teaspoon baking soda, and 1 teaspoon salt.
In a separate bowl, whisk together 3/4 cup monk fruit, 6 tablespoons ghee (melted), 6 tablespoons full-fat canned coconut milk, 3 large eggs (room temperature), and 1 tablespoon vanilla extract until smooth.
Pour the wet mixture into the dry ingredients and stir with a spatula until fully incorporated; the mixture will be very thick.
Stir in 1/2 cup + 1 tablespoon Stevia-sweetened chocolate chips and 1/4 cup black walnuts (diced) until evenly distributed. Let the batter stand 5 minutes to allow the coconut flour to absorb moisture.
Fill each muffin cup about two-thirds full using an ice cream scoop or spoon.
Bake at 350°F for 25–27 minutes, or until tops are golden brown and a toothpick inserted in the center comes out clean.
Remove muffins from the oven and let cool completely in the pan. Once cooled, run a knife around the sides of each muffin to loosen them and remove from the pan.