Preheat oven to 350°F. Line a sheet pan with parchment paper.

In a bowl combine the melted butter, peanut butter and brown sugar with a spoon (or spatula). Mixture will be grainy.

Add egg yolk and beat with spoon by hand for about 60 seconds. Mixture should lighten in color and texture.

Stir in vanilla extract

Add four, baking soda, and salt and mix until combine.

Stir in the chocolate chips.

Shape cookie dough into a large ball and place on the prepared sheet pan. Flatten slightly with the palm of your hand.

Bake until edges are dark golden brown and center has just started to turn brown, 16-19 minutes.

Let cool on the sheet pan for a few minutes, then serve warm or let cool completely on a wire rack.