Step 1

Preheat the oven to 325 degrees F (165 degrees C). Line cookie sheets with parchment paper.

Step 2

Sift together the flour, baking soda and salt; set aside. If baking at high altitude, add 2 tablespoons of flour to the flour mixture.

Step 3

In a medium bowl, cream together the melted butter, brown sugar and white sugar until well blended. Beat in the vanilla, egg, and egg yolk until light and creamy. Mix in the sifted ingredients until just blended. Stir in the chocolate chips by hand using a wooden spoon. If your butter was still hot when you added it your dough may be really wet at this point. Let it rest at room temperature for a couple of minutes if this is the case (or chill in the fridge until a little more solid) and then it will be cool enough to scoop into cookies.

Step 4

For big cookies, roll 1/4 cup balls of cookie dough and for small cookies roll 1 1/2 tablespoons of dough. Roll dough taller than wider. Bake, reversing position of cookie sheets halfway through baking, until cookies are light golden brown and outer edges start to harden yet centers are still soft and puffy, approximately 11-14 minutes for big cookie and 8-10 minutes for smaller cookies. Do not overbake. The cookies will continue to cook as they cool.

Step 5

Cool cookies on sheets until able to lift without breaking. Transfer to a wire rack to cool.