Rob and I went to Erin and Tom's  house to celebrate Tom's birthday this weekend, and Erin made an incredibly delicious chocolate chip cookie cake.
I begged her for the recipe yesterday and she told me it's the simplest thing ever. She uses cake flour and the cookie recipe on the Toll House bag of chocolate chips. She then spreads the dough evenly on a pizza pan and bakes it. She said the cake flour makes the cookie cake moist and well, cake-y.
She uses her standard crusting buttercream frosting recipe  to top it off, which makes it extra-delicious.
Here's that recipe: 
Chocolate-chip Cookie Cake
2 1/4 cups cake flour
1 teaspoon baking soda
1 teaspoon salt
1 cup (2 sticks) butter, softened
3/4 cup granulated sugar
3/4 cup packed brown sugar
1 teaspoon vanilla extract
2 large eggs
2 cups (12-oz. pkg.) chocolate chips
1 cup chopped nuts (optional)
Preheat oven to 375 degrees. Combine flour, baking soda and salt in small bowl. Beat butter, granulated sugar, brown sugar and vanilla extract in large mixer bowl until creamy. Add eggs, one at a time, beating well after each addition. Gradually beat in flour mixture. Stir in morsels and nuts.
Spread on greased pizza pan and bake 20 to 25 minutes or until golden brown. Frost when cool.