Preheat the oven to 475°F. Make sure your oven is fully preheated to ensure even baking, as this is crucial for a good cookie.

Add the dry ingredients: In a medium mixing bowl, combine the all-purpose flour, cornstarch, baking soda, white sugar, and brown sugar. Mix them well to ensure everything is evenly distributed.

Prepare the wet mixture: Take another large mixing bowl and cut the butter into half-inch chunks. Add the egg and vanilla. Mix at medium speed until the mixture is totally creamy and well combined.

Combine the mixtures: Gradually add the dry ingredients to the wet mixture in cupfuls while mixing on low speed. This helps prevent flour from flying everywhere!

Incorporate the chocolate: Once combined, gently mix in the chocolate chunks, chocolate chips, and chopped pecans using a spatula or a wooden spoon. Be careful not to overmix.

Shape the cookies: Take about 2 tablespoons of the dough and roll it into balls. If you prefer smaller cookies, use just 1 tablespoon of dough per cookie.

Prepare the baking sheet: Line a cookie sheet with parchment paper to prevent sticking. Arrange the cookie balls on the sheet, leaving about 3 inches of space between each cookie to allow for spreading.

Bake the cookies: Place the cookie sheet in the oven and bake for 9 to 10 minutes. If you made smaller cookies, reduce the baking time to 6 to 7 minutes. Look for a golden edge but a soft center.

Cool and enjoy: Remove the cookies from the oven and allow them to cool on the baking sheet for a few minutes before transferring them to a wire rack to cool completely. Enjoy the delicious aroma!