1) Preheat the oven to 350°F. Lightly grease the wells of a standard muffin pan; or line the pan with muffin papers, and grease the papers (for best release).
2) To make the cupcakes: Beat together the sugar, vegetable oil, eggs, pistachio flavor, salt, baking powder, and baking soda until thoroughly combined.
3) Whisk together the flour, pudding mix, and Cake Enhancer. Whisk together the yogurt and milk.
4) Starting and ending with the flour mixture, alternately beat in the flour and yogurt/milk: 1/3 of the flour, half the yogurt/milk, 1/3 of the flour, the remaining yogurt/milk, and the remaining flour. Beat gently to combine after each addition. Scrape the bottom and sides of the bowl, and beat briefly.
5) Stir in the chopped nuts, if you're using them.
6) Spoon the batter into the wells of the pan.
7) Bake the cupcakes for 18 to 22 minutes, until they appear set and a toothpick inserted into the middle of one of the center cupcakes comes out clean.
8) Remove the cupcakes from the oven, and as soon as you can handle them, transfer them to a rack to cool.
9) To make the frosting: Combine the cream, milk, marshmallows, pudding mix, confectioners' sugar, and pistachio flavor in a microwave-safe bowl or small saucepan. Heat gently, stirring often, until the marshmallows have melted and the mixture is smooth.
10) Remove from the heat, and chill until completely cold. Using a stand mixer or electric hand mixer, whip the frosting until it's smooth and creamy. If you've used all cream, it'll be quite stiff, which makes it perfect for piping.
11) Spread the icing (or pipe the all-cream version) atop the cupcakes. If you pipe it, you probably won't need the optional garnish of chopped nuts; if you spread the icing, chopped nuts help dress the cakes up.
Yield: 12 cupcakes.