Gluten-Free Mug Coffee Cake

Name: Gluten-Free Mug Coffee Cake
Prep time: 4 min
Cook time: 1 min
Total time: 5 min
Cuisine: American
Ingredients: 1 tablespoon butter; 2 tablespoons granulated sugar; 1 egg yolk (or use the whole egg if you're doubling the recipe to make two); 2 tablespoons milk of choice; 1/4 cup all purpose gluten-free flour blend (or Bob's Red Mill 1-to-1); 1/8 teaspoon gluten-free baking powder; 1 tablespoon butter, room temperature; 2 tablespoons all purpose gluten-free flour blend; 1 tablespoon brown sugar; 1/2 teaspoon cinnamon