To begin, preheat your oven to 350 and line two pans with parchment paper (or spray with non-stick spray).
To a large mixing bowl, add your butter, brown sugar, white sugar and cream them together with a hand mixer for a couple minutes. Add your peanut butter and blend again till smooth. Add in your egg and vanilla and lightly blend them together.
In a separate mixing bowl, add your dry ingredients and stir them together (flour, cornstarch, baking soda and salt).
Pour your dry ingredients into your wet ingredients and stir/fold them together till you have one consistent cookie dough. Add 1/2 cup of your chocolate chips and fold them into your batter.
Scoop your cookie dough onto your pans with a small cookie scoop, evenly spaced apart (no more than 12 cookies per pan). Gently flatten your cookies (with your hand or a spatula), as these don't spread much. Use the remaining 1/4 cup of chocolate chips to press a few into the top of each cookie.
Bake in the oven for 10-12 minutes, or till the edges of the cookies are just set and the center is still a touch underdone.
Let the cookies cool, then devour!
Stored in an airtight container these cookies taste best within the first 4 days. You can also freeze them (after baking) and they last for a few months.