Preheat the oven to 325 degrees and line a cookie sheet with a non-stick baking mat.

In a large bowl, mix the flour, baking soda and salt.

In a medium bowl, mix together the melted butter, brown sugar and white sugar until well combined. Add the vanilla, egg, and egg yolk and mix well.

Add the wet ingredients to the dry ingredients and stir until blended.

Form the cookie dough into individual balls that are about 1/4 cup and place them on the cookie sheet 2- 3 inches apart.

Bake for 15 to 17 minutes, or until the edges are light brown.

Let them cool on the baking sheets for a few minutes to bake just a bit more before transferring to wire racks to cool completely.