Preheat your oven to 350F and line a cookie sheet with parchment paper.
In a medium bowl, stir your dry ingredients until combined: 1¼ cups all purpose flour, 2 tbsp cornstarch, ½ tsp baking soda and ½ tsp salt. Set aside.
In a large bowl using an electric hand mixer or in the bowl of a stand mixer fitted with the paddle attachment, cream ½ cup butter and ¾ cup brown sugar until light and fluffy (about 2-3 minutes on medium speed). Add the egg and 1 tsp vanilla extract and continue to beat until incorporated.
Add your flour mixture into your butter mixture and stir on low speed until combined and no more streaks of flour remain.
Add your chopped Snickers chocolate and stir using a spatula or wooden spoon until evenly distributed.
Drop or scoop your cookie dough (a heaping tablespoonful) into your prepared pan and bake for 10 minutes or until they start to brown on the edges. Transfer the cookies to a wire rack to cool completely.
The yield/number of cookies depends on how big or small you scoop your cookie dough. I use a medium cookie scoop and make 15 cookies.
You can use regular sized Snickers chocolate bars. The minis look like they're about half the size of the regular bar so you'll need 5-6 of those.