In a large mixing bowl, combine the melted butter, granulated sugar, and brown sugar. Beat on medium speed for about 2-3 minutes until light and fluffy.

Add the large eggs and vanilla extract. Mix on low speed until well incorporated and smooth, about 1-2 minutes.

In a separate bowl, whisk together the all-purpose flour, cinnamon powder, cornstarch, baking soda, and baking powder. Gradually add to the wet ingredients, mixing on low speed just until combined.

Gently fold in the chopped pecans with a spatula. If using, fold in the optional toffee bits.

Cover the dough with plastic wrap and refrigerate for 30-45 minutes.

Preheat the oven to 350°F (175°C). Prepare a parchment-lined baking sheet.

Scoop and shape the chilled dough into balls, about 1-2 inches in diameter. Place them 2 inches apart on the prepared baking sheet.

Bake for 11-14 minutes or until the edges are golden brown. The centers should be slightly soft.

Let the cookies cool on the baking sheet for 5 minutes before transferring to wire racks.