Preheat the oven to 160 C or 325 F and line a 9×9 (or 8×8) inch baking pan with foil. Then butter it or spray with cooking spray.
In a bowl, combine the butter and sugar, mixing until well combined.
Blend in the eggs, vanilla extract and salt.
Next add in the cocoa and flour, beating to combine. The batter is incredibly thick at this stage.
Spread the mixture evenly onto the baking pan and bake for 10 minutes.
Take the brownie base out of the oven and spread the caramel on top evenly. Let it sit while you make the cookie dough.
To make the cookie dough, combine the butter, peanut butter and sugars.
Add the cream, vanilla and salt.
Next incorporate the flour. Make sure there are no air pockets.
Fold in the M&Ms, chips and oats.
Take mound-fulls of the batter, flatten them out in your palm and place them onto the caramel layer until it is covered completely. Using a knife, gently smooth out the cookie dough.
Pop this into the oven for 15-20 min.
In a saucepan, combine the chocolate and heavy cream, cooking till all the chocolate has melted. Pour on top of cookie mixture and cool completely before eating.