Preheat oven to 325 degrees F.
Melt the butter and peanut butter in a microwave safe bowl at 50% power until mostly melted. Remove from microwave and stir until the butter is completely melted and smooth, then set aside to let cool.
In a mixing bowl fitted with the paddle attachment (or using a wooden spoon), mix the cooled peanut butter and butter mixture with the sugars until fully incorporated. Beat in the egg, yolk and vanilla until combined. In a separate bowl, whisk together the flour, baking soda and salt. Gradually add to the sugar/butter mix until a dough forms. Fold in the chocolate chips.
Roll just under golfball sized portions of dough and place on cookie sheets two inches apart. Bake for 10 to 12 minutes, or until the edges are golden, rotating halfway during baking. Do not over bake. Remove from oven and cool for 10 minutes on the cookie sheets, then transfer to wire racks to cool completely.
Source: Adapted from How Sweet It Is