Arrange 1 oven rack at lowest rack setting; place second rack in middle of oven. Preheat oven to 425°. Place potatoes in a greased 15x10x1-in. baking pan. Drizzle with oil; sprinkle with 1/2 teaspoon salt. Toss to coat. Roast until tender, 20-25 minutes, stirring occasionally.
In a large bowl, mix yeast, remaining 1 teaspoon salt and 2 cups flour. Add warm water; beat on medium speed until smooth. Stir in enough remaining flour to form a soft dough (dough will be sticky). Turn dough onto a floured surface; knead until smooth and elastic, 6-8 minutes. Gently knead in roasted potatoes and cheese. Place in a greased bowl, turning once to grease the top. Cover and let rise in a warm place until doubled, about 1 hour.
Punch down dough. Shape into a 7-in. round loaf. Place on a parchment-lined baking sheet. Cover with a kitchen towel; let rise in a warm place until dough expands to a 9-in. loaf, about 45 minutes.
Place an oven-safe skillet on bottom oven rack. Meanwhile, in a tea kettle, bring 2 cups water to a boil. Using a sharp knife, make a slash (1/4 inch deep) across top of loaf. Place bread on top rack. Pull bottom rack out by 6-8 in.; add boiling water to skillet. (Work quickly and carefully, pouring water away from you. Don’t worry if some water is left in the kettle.) Carefully slide bottom rack back into place; quickly close door to trap steam in oven.
Bake 10 minutes. Reduce oven setting to 375°. Bake until deep golden brown, 30-35 minutes longer. Remove loaf to a wire rack to cool.