Grease 13x9 pan with cooking spray, set aside and do not preheat oven.
Chop apples into small chunks, this will create about 2 1/2 cups of apples; set aside.
In a large bowl or stand mixer, beat sugar, eggs, vanilla extract and oil until smooth.
In a separate bowl sift flour, salt, and baking soda together.
Slowly mix flour mixture into egg mixture until well combined.
Add half of the chopped apples and toffee bits into batter and stir, then add the remaining apples and toffee bits. Gently stir until apples are evenly mixed in.
Spread batter into prepared pan and place in cool oven. Bake for 50 to 55 minutes in a 325 degree oven; allow pan to cool.
For the caramel topping:
In a small saucepan heat sugars, butter, and evaporated milk until boiling. Stir constantly for 2-3 minutes until sauce thickens. Stir in vanilla.
Pour caramel topping over cake, allow the caramel to slightly cool for a minute or two then top with toffee bits.