Make the Dough
In the bowl of a standing electric mixer fitted with the paddle, beat the yeast mixture with the mashed potatoes, 3 tablespoons of the olive oil, 2 teaspoons of salt and the remaining 3 cups of flour at medium speed for 2 minutes. Switch to a dough hook and knead until a soft, slightly sticky dough forms, 5 minutes. Transfer the dough to a lightly oiled bowl; turn to coat. Let stand, covered, in a warm, draft-free spot until doubled in bulk, about 1 hour.