Heat oven to 350 degrees F* (see note about oven temp). Line a baking sheet with parchment paper or a silpat baking mat.

Melt the butter for about 45 seconds in the microwave, until it's almost completely melted. Remove and stir it, allowing any remaining butter to melt. Allow the butter to cool until it's almost room temperature, but still a liquid.

Add melted butter and both sugars to a mixing bowl and mix until well combined. Add the egg, egg yolk, and vanilla and stir combined.

In a medium bowl mix together flour, salt, and baking soda.

Stir the dry ingredients into the bowl with the wet ingredients and begin to mix. Add chocolate chips, stirring just until combined. The dough will be soft. Refrigerate dough for 30 minutes or up to 2 days (or freeze for longer).

Scoop dough into balls and place on a cookie sheet. Bake for 8-14 minutes (depending on size) or until set on top. Cool for 10-15 minutes on a baking sheet before moving to a wire cooling rack.