Melt the butter in a microwave or double broiler, stir in vanilla. Cool completely. In a large bowl, combine the flour and sugar, stir in butter mixture and chocolate chips, the mixture will be crumbly. Shape into 1 inch balls. Place 2 inches apart on ungreased baking sheets, flatten slightly. Bake at 375ºF. for 12 minutes or until the  edges begin to brown. Cool on wire racks. Yield about 4 dozen