Brown Sugar Toffee Cookies

2 1/4 cups all-purpose Gold Medal flour
2 teaspoons baking soda
1 teaspoon cornstarch
1/2 teaspoon salt
1/2 teaspoon ground cinnamon
3/4 cup unsalted butter, at room temperature
1 1/4 cups dark brown sugar
1 large egg
1 teaspoon vanilla extract
1 cup Heath toffee bits
Extra dark brown sugar for rolling cookies, about 1/2 cup