Preheat oven to 350 degrees F. Lightly grease two 15x10x1 baking sheets with baking spray and set aside.
Prepare one cake mix at a time. Combine one cake mix, 3 eggs, 1 cup water, 2 tbsp vegetable oil, 2 tbsp cocoa powder and 1/2 cup sour cream in a large bowl and mix on low speed for 30 seconds. Increase speed and mix until fully combined, scraping down sides of bowl if needed. Pour cake batter into baking sheet, spread to an even layer and bake for 18 to 20 minutes or until toothpick inserted in center comes out clean. Let cool completely. Repeat with other cake mix.
Use a circular cookie cuter to cut the shapes needed to fill your plastic cups or trifle dish. Cut 2 circles per cup.
Place one circle in the bottom of the cup. Combine the sweetened condensed milk and caramel sauce in a large bowl and spoon one tablespoon over the top of the bottom layer, or if making one large truffle, use half of the mixture.
Sprinkle 1 tsp of toffee bits on top of the coated cake and then top with a layer of Cool Whip, followed by another layer of cake, caramel mixture and more Cool Whip.
Top each trifle with more toffee bits and then drizzle with the hot fudge sauce. Refrigerate until ready to serve. Enjoy!
Notes
If you prefer to make one large trifle, you could probably get away with just baking one cake mix and making it into two 8" rounds.