These cupcakes have a secret ingredient, one you definitely wouldn't expect - plain mashed potato! All you need to do is boil up a peeled buttery Yukon Gold, drain the water away and mash it as smooth as you can get - don't use leftover mashers that have been seasoned with who knows what. You do want this to cool down before you use it - be sure to start this process before you get anything else for the cupcake batter ready.
The potato adds plenty of moisture, allowing you to cut back on the fat a bit, without compromising the texture of the cupcake. To keep the crumb tender and soft, yet still add nutritional boost, we used a combination of flours - equal parts of soft cake flour and whole-wheat pastry flour. When we have add-ins to batters, fresh blueberries in this case, add them when most of the flour has been moistened, yet you still see some dry flour-y spots. This way, you'll finish incorporating the batter and get the blueberries worked in, without worry of over-working the mixture.
Cupcake batter typically fills the baking tins about two-thirds full when all is said and done, but be prepared to fill them right up to the top with this recipe. These cupcakes are done when they either spring back when lightly pressed in the center or a toothpick comes out with a few moist crumbs attached when inserted in the center - both methods work well, just use whichever you are most comfortable with! Whisk the muffins out of the tin as soon as you can fingers can stand it - try not to leave in any longer than 5 to 10 minutes as the bottoms will steam and become tough.
The frosting for these cupcakes is very cloud-like being light and fluffy, almost marshmallowy, with a tinge of color and flavor coming from a couple scoops of blueberry preserves. I did press our preserves through a fine mesh strainer so we'd end up with a smooth color, but feel free to skip that or use a blueberry jam. You won't have to be skimpy with this icing at all either - because it is so airy, you'll have plenty to go around, adding a small mountain on top of each cupcake. The frosting does stiffen as it sits - be sure to get it onto the cupcakes as soon as you make it.
Because we know where we get our eggs from, it didn't bother us in the least to use them in the frosting. However, if you get squeamish with the thought of using egg whites like this, you could either try using pasteurized eggs or use dried egg whites, reconstituting them according to the directions on the package (using enough to make up 2 whites). If you're a fan of the blueberry and coconut mash up, you can infuse a bit of coconut flavor into these golden cupcakes by swapping out the vanilla for about 1/2 teaspoon coconut extract in the batter, then add 1/4 teaspoon to the frosting as well.