1/2 cup butter
1 cup light brown sugar
2 1/2 cups white sugar
1 teaspoon vanilla extract
1/2 cup milk
3 cups chocolate chips
Preheat oven to 350 degrees F (175 degrees C). Line a 9x9 inch pan with foil or aluminum foil.
In a large saucepan, over medium heat, combine butter, brown sugar, white sugar, vanilla and milk. Bring to a boil, stirring occasionally, until butter melts and mixture is thickened, about 5 minutes. Reduce heat to medium and stir in chocolate chips. Pour into foil prepared pan.
Bake in preheated oven for 3 hours, or until crisp and golden brown. Serve warm or cold. Cool before cutting into bars.