Heat oven to 350ºF. Line 6 medium muffin cups with paper baking cups; or grease cups with shortening or spray with cooking spray. In large bowl, stir flour, brown sugar and butter with spoon until crumbly. Reserve 1/3 cup mixture for topping.
Stir egg, baking powder, cinnamon and milk into remaining crumbly mixture until well mixed. Spoon batter into muffin cups. Sprinkle reserved crumbly mixture over batter.
Bake 20 to 30 minutes or until toothpick inserted in center comes out clean. Cool 5 minutes; remove from pan. Sprinkle warm cakes with powdered sugar before serving. Serve warm or cooled.