From America's Test Kitchen
Mashed potatoes are hefty and substantial, but in a potato rolls recipe, they give the crumb a light, tender, moist texture. That’s because the starches in potatoes dilute the gluten-forming proteins, which weakens the structural network and makes it softer, moister, and more tender. For the lightest potato rolls, we use a combination of ½ pound of mashed russet potatoes and high-protein bread flour. This creates a potato roll dough with a stable structure that supports the greatest amount of potatoes, producing rolls that were not only perfectly risen but also light and airy.
Makes 12 Rolls
Don’t salt the water in which you boil the potatoes. A pound of russet potatoes should yield a little more than one firmly packed cup (1/2 pound) of mashed potatoes. To ensure optimum rise, your dough should be warm; if your potatoes or potato water is too hot to touch, set it aside to cool before proceeding with the recipe. Bread flour is best for this recipe; do not attempt to substitute all-purpose flour. This dough looks very dry when mixing begins, but resist the urge to add more water; the dough will soften as mixing progresses. If you prefer, you may portion the rolls by weight in step 5 (2 ounces of dough per roll).