In a large mixing bowl combine the softened butter, powdered sugar, brown sugar and salt. Beat with an electric mixer until light and smooth.

Add the vanilla and beat until combined.

Sift in the flour and mix until no white flour is visible and the dough is clumpy and crumbly.

Add both of the chocolate chips and mix one last time. The dough should still be clumpy and crumbly.

Turn the dough out onto a large piece of wax paper or parchment. Use your hands to press and shape the dough into one cohesive rectangle. Take extra care of the edges, try to press any shaggy pieces in.

Place a second sheet of wax paper on the top of the dough. Use a rolling pin to roll the dough out between the two pieces of wax paper. Roll the dough to an even rectangle roughly 1/2" thick, and 11.5" x 8.5" in size.

Slide the dough onto a cutting board and place in the refrigerator for about 30 minutes or until the dough has chilled and hardened.

Use a sharp knife to trim the uneven edges of the rectangle. Cut the dough in half the long way, then make horizontal cuts about every inch or inch and a half. Each cookie should measure roughly 1" x 4". If the dough is too hard and difficult to cut, let the dough sit for a few minutes to soften.

Transfer the cookies to a parchment lined baking sheet, and bake in the preheated oven for 20-25 minutes or until the edges are just beginning to turn lightly golden.

Remove the cookies from the oven and carefully transfer to a cooling rack. Let cool completely.

Serve and enjoy! Store leftovers in an airtight container for up to a week.