Royal Rhubarb Coffee Cake

Ingredients

• 1/3 cup butter (softened)
• 1 cup sugar
• 1 egg
• 1 tsp vanilla extract
• 2 cups all-purpose flour
• 3 tsp baking powder
• 1/2 tsp salt
• 1 cup milk
• 3-1/2 cups rhubarb (fresh or frozen, thawed and drained)
• 3/4 cup packed brown sugar
• 1/4 cup butter (melted)
• 1 tsp ground cinnamon