Preheat the oven to 350° F.
Cream together the butter, granulated sugar and brown sugar.
Add the egg and vanilla. Mix until light in color and creamy.
Add in the dry ingredients (flour, baking soda and salt), mix into the dough. Mix until completely combined. The dough will be soft.
Gather the dough into one large ball and place in the center of a greased cookie sheet or pizza pan.
Press the cookie dough down and into a large flat circle.
Bake at 350° for 12-15 minutes or until the center no longer looks wet and glossy and the entire cookie pizza has puffed up.
Allow the cookie pizza to cool before cutting. Decorate with frosting and sprinkles, if desired.