Preheat the oven to 350°F (175°C) and line a muffin tin with cupcake liners.
In a large mixing bowl, whisk together the dry ingredients: gluten-free flour, sugar, cocoa powder, baking powder, baking soda, and salt.
In another bowl, mix the wet ingredients: melted butter, eggs, vanilla extract, and milk until smooth. Pour into the dry ingredients and stir gently until just combined. Fold in chocolate chips if desired.
Fill each cupcake liner about two-thirds full with batter.
Bake for 18-20 minutes, or until a toothpick inserted comes out clean.
Allow the cupcakes to cool in the pan for 5 minutes, then transfer to a wire rack to cool completely.