Cupcakes:
1 large egg
3/4 cup loosely packed brown sugar
2 teaspoons vanilla extract
1/2 cup unsalted butter (1 stick), melted and cooled
1 1/4 cups all-purpose flour
1/2 cup old-fashioned rolled oats
1 1/4 teaspoons baking soda
1/4 teaspoon salt
1/4 teaspoon cinnamon
2 tablespoons milk
1/2 cup chocolate chips, tossed in a sprinkle of flour

Frosting:
1 cup unsalted butter (2 sticks), softened
2 cups powdered sugar
1/2 cup loosely packed brown sugar
1/4 teaspoon cinnamon
1 tablespoon vanilla extract
1 tablespoon of milk, if needed
1/3 cup mini chocolate chips