Preheat the oven to 350 degrees F. Add cupcake liners to two 12 serving cupcake pans and set aside.
In a large mixing bowl, add gluten-free flour, sugar, baking powder, baking soda and salt. Whisk to combine.
In that same bowl, add eggs, milk, oil and vanilla extract. Use a hand mixer to beat the ingredients for 2 minutes. Stir in the boiling water until a smooth consistency is reached.
Use a large cookie scoop to equally portion the batter into the liners of the prepared cupcake pans. Bake for 20-22 minutes or until a toothpick inserted in the center of a cupcake comes out clean.
Remove cupcakes from the oven and place on a wire cooling rack to come to room temperature.
While cupcakes cool, prepare the frosting: Add room temperature butter to the bowl of a mixer fitted with whisk attachment (or large mixing bowl if using a hand-held mixer). Mix on high until a creamy consistency is reached. Add powdered sugar, cocoa powder, milk, salt and vanilla extract. Mix on low for 30 settings. Increase speed to high for 1 minute.
Spoon frosting into a piping bag fitted with a large star tip. Pipe frosting onto cooled cupcakes, garnishing each one with sprinkles.