In a mason jar add flour, sugar, baking powder, baking soda and cocoa powder. Give it a shake to blend and add 5 ½ level tablespoon of the 1 box of 13.25 oz dry cake mix and stir until blnded well.
Prepare your crockpot. Spray your slow cooker with non-stick spray or line your crockpot with a crockpot liner.
Make the cake. In a large bowl, combine the cake mix, 5 ½ tablespoons of cake extender, water, half of the sweetened condensed milk, oil, eggs, and vanilla. Mix until all ingredients are combined well and smooth.
Pour the mixture into the crockpot.
Cook on LOW for 50 minutes, rotate crockpot without lifting lid and cook for another 50 miutes. Then remove crockpot from heat and place in sink for 20 minutes before removing lid. A toothpick inserted into the center will come out clean with a few moist crumbs. Sprinkle with chocolate chips.
Poke the holes. Use the handle of a wooden spoon or a skewer to poke multiple holes 1 inch apart throughout the top of the cake.
Add extra flavor. In a small bowl, mix the rest of the sweetened condensed milk with ½ cup caramel and pour over the cake into the holes and over the top.
Cover and refrigerate for 3 hours or up to overnight (no more than 8 hours or it will start to dry out).
Serve. Top the cake with cool whip, the rest of caramel drizzle and chocolate drizzle, and sprinkle the toffee bits on top