Step 1

Heat oven to 350 degrees F (177 degrees C).

Step 2

Mix together the butter and sugars in a small mixing bowl.

Step 3

Add the egg yolk and the vanilla and continue mixing until well combined.

Step 4

Add in the flour, baking soda, and salt to the bowl and stir until just combined.

Step 5

Fold in the chocolate chips and chopped walnuts.

Step 6

Pour cookie dough into a buttered 10-ounce ramekin or spoon cookie dough onto a cookie sheet.

Step 7

Bake for 22-25 minutes or until top is golden and the edges of the cookie is set.

Step 8

Remove from the oven and place on a cooling rack to cool for 10 minutes.