In a large (10 inch) cast iron skillet, melt the butter.
Add the brown sugar and granulated sugar and stir until dissolved.
Allow this to cool down until it is just warm.
Add 2 beaten eggs.
Stir in 2 teaspoons vanilla.
Mix the flour, baking soda and salt with a whisk.
Stir in the flour mixture with the butter and sugar mixture. The batter will become thick.
Stir in the butterscotch chips, chocolate chips, and toffee bits.
Press the batter down into the skillet.
Bake for 25 to 30 minutes at 375 degrees.