In a large bowl, cream together melted unsalted butter, granulated sugar, and brown sugar using a hand mixer until light and fluffy, about 2-3 minutes.

Add in the egg and vanilla extract to the butter-sugar mixture, then beat until well combined and smooth for 1-2 minutes.

In a separate bowl, whisk together the all-purpose flour, cornstarch, baking soda, baking powder, and cinnamon. Gradually mix these dry ingredients into the wet ingredients, stirring gently.

Fold in the chopped pecans and optional toffee bits into the cookie dough until evenly distributed.

Refrigerate the dough for about 30-45 minutes.

Preheat oven to 350°F (175°C). Shape the dough into 1-inch balls and arrange on a parchment-lined baking sheet.

Bake for 11-14 minutes, until golden around the edges but still soft in the center.

Allow cookies to cool on the baking sheet for 5 minutes before transferring to a wire rack.