Preheat your oven to 350°F (175°C) and grease the bottom of a 9x13-inch glass pan.

In a large bowl, combine the cake mix, water, vegetable oil, and eggs with a mixer on medium speed until smooth. Transfer the batter to the prepared pan and bake for 30 to 35 minutes, or until a toothpick inserted in the center comes out clean. Let the cake cool on a wire rack for 5 minutes, then make shallow slits across the top, ensuring not to cut all the way through to the bottom.

While the cake is cooling, heat the sweetened condensed milk and 6 ounces of caramel topping in a saucepan over low heat, stirring until smooth. Pour this mixture evenly over the warm cake, letting it soak in. Reserve 1 to 2 tablespoons of the chopped chocolate-covered toffee for garnish, and sprinkle the remaining toffee over the cake.