Preheat the oven to 350°F. Line a muffin pan with cupcake liners.
Sift the cocoa powder, almond flour, oat flour, potato starch, and powdered sugar into a large bowl and mix well to combine. Set aside.
Put the milk chocolate chunks and butter in a small pan over low heat and melt gently, stirring constantly with a spoon. Remove from the heat and set aside for 10 minutes to cool. Add the eggs and mix until combined.
Stir the dry ingredients into the chocolate mixture using an electric hand mixer. Fold in the chocolate chips.
Spoon the batter into the liners and bake for 25 minutes.
Cool the muffins and serve.
Tip: These freeze really well and can be kept in the freezer for up to 3 months. If you don't have a jumbo muffin pan, these can also be made in a standard 12-cup muffin tin.