Preheat oven to 300°F (150°C).

In a large bowl, cream together butter, brown sugar, and vanilla using an electric mixer until light and fluffy.

Add flour and cornstarch to the mixture.

Mix until a smooth dough forms.

Gently fold in mini chocolate chips, if desired.

Pour granulated sugar into a small bowl for dipping.

Butter the bottom of a small glass and dip it in sugar.

Roll tablespoon-sized portions of dough into balls.

Place the dough balls on a cookie sheet.

Flatten each cookie with the sugar-coated glass.

Bake for 20 minutes, or until the edges are lightly browned.

Let cookies cool for 5 minutes on the cookie sheet to prevent crumbling before transferring to a wire rack to cool completely.