Preheat oven to 350 degrees and line a baking sheet with a silicone, non-stick baking liner or parchment paper. Set aside.

In a medium sized bowl combine flour, corn starch, baking soda and salt. Set this aside, too.

Cream butter for 1-2 minutes until nice and soft.

Add sugar and brown sugar, creaming again for ~2 minutes. Be sure to scrape the edges so it's all incorporated and there aren't any large butter chunks.

Now add in egg, egg yolk, and vanilla. Continue to mix until combined well.

Slowly add in your flour mixture to the butter mixture, 1/3 at a time. Your dough will be thick, this is good!

Next, fold in your candy pieces until evenly distributed.

Take ~2 tbsp of the dough, form it into a tall ball (I like to use a cookie scoop for this!) I try to make mine almost twice as tall as they are wide, this prevents them from getting flat. Then, place on your prepared cookie sheet.

Bake your cookies at 350 for ~9 minutes.

Once cookies come out of the oven allow them to cool for ~2 minutes on the sheet then transfer them to a cooling rack to finish cooling.

Enjoy!