In a medium mixing bowl beat the butter, superfine sugar, brown sugar, and salt until light and fluffy.
Using a wooden spoon, mix in the flour. The dough may be crumbly, but as long as it presses together and holds its shape, it's ready to go in the pan.
Press into the prepared pan and bake for 15 minutes or until the edges are lightly browned
Meanwhile, in a medium saucepan heat the condensed milk and butter over medium heat stirring constantly until bubbly.
Cook and stir for 5 minutes until the mixture becomes smooth and thick. Stir in the vanilla and salt.
Spread over baked base and bake for 12-15 minutes more or until golden.
Remove from the oven and sprinkle the chocolate chips evenly over the hot base. let stand 2-3 minutes to soften and then spread evenly over the toffee layer.