- 3/4 cup warm water (105° to 115°)
- 1 1/4 tsp. active dry yeast
- 1/2 tsp. sugar
- 1 1/2 cups flour, plus more for kneading the dough
- 3/4 tsp. salt
- 2 tbsp. olive oil, plus more for greasing the bowl
- 2 tsp. chopped fresh rosemary leaves
- 6 tbsp. grated Parmesan
- 2 1/2 cups leftover mashed potatoes
1. In a medium bowl, mix the water, yeast, and sugar. Let stand until foamy, about 10 minutes.
2. In a large bowl, mix 1 1/2 cups flour and the salt. Make a well in the center of the flour. Stir in the yeast mixture. Transfer the dough to a lightly floured work surface. Knead the dough, dusting with flour if it gets too sticky, until it is smooth and springy, 7 to 8 minutes. Transfer to a lightly oiled bowl and turn the dough until coated. Cover tightly with plastic wrap. Let the dough rest in a warm, draft-free area until doubled in size, 1 to 1 1/2 hours.
3. In a small bowl, microwave 2 tbsp. oil and the rosemary on high until fragrant, about 20 seconds. Strain and reserve the oil. Stir the rosemary leaves and half the cheese into the potatoes.
4. Preheat the oven to 450°. On a lightly floured rimmed baking sheet, roll or stretch the dough out to the edges. Brush the dough with half the rosemary oil. Bake until the crust is light golden, about 10 minutes. Spread the potatoes on the crust, leaving a 3/4-inch border. Top with the remaining cheese. Bake until the crust is browned, about 10 minutes more. Drizzle with the remaining rosemary oil.