Mix up the dry ingredients and then the wet ingredients. You'll set the Coffee Cake Muffin batter to the side.
In a smaller bowl, mix together the crumble topping--the best part.
Layer the batter with the crumble mixture. The layers will be: Batter, crumble, batter, crumble.
Make the frosting for the top. Drizzle over the cooled muffins.