Chocolate Chocolate Chip Cookies

1 cup butter, softened
1 1/2 cups white sugar
2 eggs
2 teaspoons vanilla extract
2 cups all-purpose flour
2/3 cup cocoa powder
3/4 teaspoon baking soda
1/4 teaspoon salt
2 cups semisweet chocolate chips
1/2 cup chopped walnuts (optional)

1. Preheat oven to 350° F (175° C).

2. In large bowl, beat butter, sugar, eggs, and vanilla until light
and fluffy. Combine the flour, cocoa, baking soda, and salt. Stir
into the butter mixture until well blended. Mix in the chocolate
chips and walnuts. Drop by rounded teaspoonfuls onto ungreased
cookie sheets.

3. Bake for 8 to 10 minutes in the preheated oven, or just until
set. Cool slightly on the cookie sheets before transferring to wire
racks to cool completely.
　
Variations & Tips:
- I used 1 cup whole wheat flour and 1 cup all purpose (white) flour.
- Instead of all white sugar, I used 3/4 cup brown sugar & 3/4 cup white sugar.
- I mixed big and little chocolate chips, using 1 cup mini and 1 cup standard size.
- Eight minutes seemed to be the perfect baking time in my oven. They didn't seem quite done, but were so soft in the middle after they were cooled.