Preheat oven to 350 degrees, line a cupcake pan with paper or foil liners. You can have another small pan lined with 4 more liners if you have one to use, otherwise when the others are cooling out of the pan you can line the last 4 muffin tins with the paper liners.In a large mixing bowl, combine cake mix, pudding mix and egg whites.Start pouring in the seltzer. Mix well and add vanilla extract. Switch over to your electric mixer and mix until the batter is fluffy and smooth.Cover the batter and place in fridge for about 20 minutes. This step is very important as the cupcakes will end up being larger in the end.Remove batter from the fridge, and using an ice cream scoop, fill each tin 3/4 (or almost to the top). Do not fill to the very top or over fill. Tap the pan gently once or twice on the rack in the oven just to loosen any air bubbles.Bake for about 15-20 minutes or until a wooden skewer or toothpick comes out clean or with a few dry crumbs. During baking, turn pan around for even baking after about 7 or 8 minutes.Let cool in pan on wire cooking rack for about 15 minutes, then take them out and cool directly on the cooling rack.Bake your next 4 cupcakes and follow directions above.Let the cupcakes cool completely.In the meantime, get your frosting ready. Mist a measuring cup with cooking spray and add the Fluff; scoop out Fluff and add to a medium mixing bowl.Start mixing Fluff with 2 teaspoons of milk with a small wire whisk until frosting reaches a spreading consistency. You may need to add another teaspoon or two of milk. The frosting will be thin.Scoop a tablespoon of frosting over each cupcake. You can spread with the spoon, a butter knife or small spatula. When they are all done, sprinkle the nuts over each cupcake. Enjoy!