Start by preheating your oven to 350°F (175°C). This ensures that your cookies bake evenly and come out perfectly golden.
In a large mixing bowl, use a whisk or an electric mixer to cream together the softened unsalted butter, light brown sugar, and granulated sugar until the mixture is light and fluffy. This process typically takes about 2-3 minutes.
Beat in the large egg and vanilla extract until fully combined. Make sure to scrape down the sides of the bowl to incorporate all ingredients.
In a separate bowl, whisk together the all-purpose flour, cornstarch, baking soda, and a pinch of salt. Gradually add this dry mixture to the wet ingredients, mixing until just combined. Be careful not to overmix!
Gently fold in the diced Snickers and semi-sweet chocolate chips using a spatula. This is where the magic happens—make sure every cookie has a bit of that Snickers goodness!
Using a cookie scoop or a tablespoon, drop rounded balls of dough onto the prepared baking sheet, leaving space between them to allow for spreading.
Bake in the preheated oven for 10-12 minutes, or until the edges are lightly golden but the centers still look soft. They will continue to cook on the baking sheet once removed from the oven.
Let the cookies cool on the baking sheet for about 5 minutes before transferring them to a wire rack to cool completely. This step is crucial for achieving that perfect chewy texture!