In a stand mixer cream butter and both sugars together until light and fluffy, about 2 minutes. Mix in the egg and vanilla. Add flour, cornstarch, baking soda and salt. Mix until everything is combined.
3/4 cup unsalted butter, 3/4 cup light brown sugar, 1/4 cup granulated sugar, 1 whole large egg, 2 teaspoons vanilla extract, 2 cups all-purpose flour, 2 teaspoons cornstarch, 1 teaspoons baking soda, 1/2 teaspoon salt
Fold in 1 1/2 cups of red, white and blue M&M's
2 cups red
Scoop golf ball sized balls of dough onto a baking sheet. Top each ball of dough with the remaining 1/2 cup candy. Chill for 30 minutes.
Preheat oven to 350º F.
Bake for 10-11 minutes, until the edges are set, the tops are golden and appear dry.
Remove from the oven and let cookies cool for 5 minutes before removing to a wire rack.
Notes
You can use white chocolate chips with red & blue M&M's. You just want a total of about 2 cups.