Mix brown sugar and flour thoroughly; cut in butter until of consistency of coarse meal.
Reserve 1 cup mixture; add salt and soda to remaining mixture.
Blend in egg, milk and vanilla; beat well.
Pour into well-greased 9 x 13-inch baking dish.
Chop toffee bars coarsely.
Sprinkle batter with reserved mixture, nuts and toffee bars.
Bake at 350 degrees for 35 minutes.