Whisk together the flour, baking soda, cornstarch, and salt until well combined. Set aside.
In a large bowl, beat together the butter and brown sugar until light and fluffy.
Add the egg and vanilla extract and beat to combine.
Add the dry ingredients and mix until well combined. NOTE: the dough will be thick.
Fold in the mini chocolate chips and toffee bits.
Use a tablespoon or 1 tablespoon cookie scoop to scoop out balls of dough. Roll the balls between your hands to smooth them, then place the balls on a plate or baking sheet and chill for at least 2 hours.
When ready to bake, preheat the oven to 350 degrees. Line a baking sheet with parchment paper and place the dough balls two inches apart on the prepared pan.
Bake in the preheated oven for 10 to 12 minutes, until the edges are just beginning to brown.
Allow the cookies to cool for 5 minutes on the pan, then transfer to a wire cooling rack to cool completely.
Notes
Pro TipsDon't skip chilling the cookie dough! This makes a big difference in the final flavor, form and texture. Use a 1-tablespoon cookie scoop for scooping the dough. It will go faster, be less messy and all the cookies will be the same size.Storing the cookiesStore in an airtight container at room temperature for up to 4 days.To freeze them: after they cool, place in a freezer safe airtight container and freeze for up to 3 months.