Melt 1 cup morsels and butter in large saucepan over low heat; stir until smooth. Remove from heat. Stir in eggs. Stir in flour sugar, vanilla, and baking soda. Stir in remaining chocolate morsels. Spread batter in prepared greased pan.
Bake for 15-25 mins depending on pan size, or until toothpick comes out slightly sticky.