Preheat Oven: Set your oven to 350°F (175°C). Prepare your donut pans by greasing them.

Mix Dry Ingredients: In a large bowl, combine the gluten-free flour, cocoa powder, light brown sugar, baking powder, and salt.

Prepare Wet Ingredients: In another bowl, mix melted butter (or vegan baking sticks) with milk and the cornstarch-water mixture. Add vanilla extract.

Combine Ingredients: Gradually mix the wet ingredients into the dry ingredients until well combined.

Fill Donut Pans: Pour the batter into the prepared donut pans.

Bake: Bake for about 20 minutes, or until the donuts are golden brown.

Cool: Let the donuts cool in the pan for a few minutes, then transfer them to a wire rack to cool completely.

Prepare Glaze: In a bowl, mix confectioners' sugar with water and vanilla extract until smooth.

Glaze Donuts: Dip each cooled donut into the glaze and let the excess drip off. Add sprinkles if desired.