THE BEST CHOCOLATE CHIP COOKIE BARS

I constantly need a quick treat for something here.  I have pretty much given up baking individual cookies.  I have made these cookie bars several times and tweaked them a little here and there until I think they are just about perfect...at least for the Canary Islands.
The recipe makes about 3 dozen bars.  They are always a hit.

Remove 2 T. of butter from a cube of butter (6 T.) and melt a little in a glass mixing bowl.

Add and beat with a hand beater:
2 T. Vegetable oil (it makes a moister cookie with the butter).
2 eggs
1/2 C. Brown sugar
1 C. White sugar
1 tsp. Vanilla

Stir In and mix well:
1/2 tsp. Baking Powder
1 tsp. Baking Soda
2 C. Flour
2 T. Cornstarch

Add and stir:
1 C. Chocolate Chips or chopped chocolate if you are in Europe
1 C. chopped walnuts, if desired

Spread into a sprayed 9x13 pan and bake at 350 for 20-25 min. A glass pan will bake hotter so turn the oven to 325.  Don't overbake.