1 cup unsalted butter, softened
3/4 cup firmly packed light brown sugar
1/2 cup granulated sugar
2 large eggs
1 teaspoon pure vanilla extract
1 1/2 cups all-purpose flour
1 teaspoon baking soda
1 teaspoon ground cinnamon
1/2 teaspoon salt
3 cups quick or old fashioned oatmeal
3/4 cup (1 1/2 sticks) cup unsalted butter, softened
2 1/2 cups confectioners' sugar, sifted
1 teaspoon pure vanilla extract
1 tablespoon milk or half and half