Preheat oven to 350 degrees. Line 18 standard muffin tins with cupcake papers.

In the bowl of an electric mixer combine the eggs, water, and oil. Beat on medium speed for 2 minutes. Turn off mixer, add the pistachio pudding mix and beat until combined. Turn the mixer to low and gradually add the cake mix. Beat until just combined. With a rubber spatula, scrape the sides and bottom of the mixing bowl to make sure all the ingredients are uniformly combined. Divide the batter among the prepared muffin tins filling about 2/3 full. Bake for 22 – 26 minutes or until the cupcakes spring back when touched lightly and a toothpick inserted in the center comes out clean. Let cool completely. Remove the liners from the cupcakes and slice in half horizontally.

While the cupcakes are baking and cooling, prepare the frosting.

For each cupcake in a jar place a cupcake half (use the bottom halves in the bottom of the jar) pipe on or spoon in some frosting, add another cupcake half, another layer of frosting, one more cupcake half (use a top for the final layer) and one more layer of frosting. Sprinkle the top with some chopped pistachios.