Peel potatoes and cut crosswise into 3/4-inch-thick slices. Rinse potatoes well and pat dry between paper towels.
Heat butter in a 12-inch nonstick skillet over moderately high heat until foam subsides, then brown potatoes in 1 layer, turning over carefully, about 4 minutes per side.
Add saffron-infused water, salt, and pepper and briskly simmer, uncovered, over moderate heat 5 minutes. Reduce heat to moderately low and simmer until potatoes are tender and water is evaporated, about 15 to 20 minutes more.
