Make cake mix in two 8-inch round cake pans according to package instructions. Cool completely and cut into 1- inch cubes.
In a mixer, fitted with a whisk attachment, whisk the mascarpone cheese. Slowly add the heavy cream and whisk on high making sure the cream is incorporated into the cheese. Scrap down the sides of the bowl periodically. Whisk until the mixture is thick and forms soft peaks. Add the vanilla and sugar, mix.
In a trifle bowl, measuring approximately 8½ inches high and 5 inches wide, layer 1/3 jar of SWK Dulce de Leche, one half of the cake cubes, ¼ of the mascarpone cream, 1 sliced banana, and sprinkle with 1/3 of the toffee bits and 1/3 chopped chocolate bar. Repeat these layers. Finish layering with ¼ of the cream filling, sliced banana the remaining 1/3 Dulce de Leche, then the rest of the cream filling topped with the rest of the toffee and chopped chocolate.