Preheat oven to 350F. Line a 9" pan with parchment or aluminum foil and spray with cooking spray.
Combine the melted butter, brown sugar and vanilla in the bowl of a stand mixer and mix to combine well.
Add the flour, oats, baking soda and salt and stir to combine.
Press half the mixture into the pan and smooth it evenly with a measuring cup. Bake for 8 minutes.
Meanwhile combine the caramels and cream in a pot and melt gently over medium low heat stirring frequently until smooth.
When the base layer is done, sprinkle with chocolate chips and toffee pieces.
Pour the caramel over and spread evenly.
Spread the remaining oat mixture over the top and bake for 18 more minutes.
Let the bars set for a couple hours before cutting. They set up better the longer they sit. For neater squares, make them the night before and cut in the morning.
