Combine cumin, coriander, turmeric, and cayenne together in a small bowl for spice mix; mix well.

Cut russet potatoes in half, then into quarters, eighths, and sixteenths.

Bring a large pot of well-salted water to a boil over medium-high heat. Add potatoes and 2/3 of the spice mixture and continue to boil until just tender and fairly easily pierced with a knife, about 10 minutes. Drain; transfer to a plate and let cool to room temperature, about 30 minutes.

Wrap potatoes in plastic and refrigerate until thoroughly chilled, 8 hours to overnight.

Remove potatoes from the refrigerator and cut in half once more.

Heat butter and olive oil in a nonstick skillet over medium to medium-high heat. Add potatoes and season with salt. Cook until crisped, 3 to 5 minutes. Toss with a spatula and continue to cook until golden brown, 3 to 5 minutes more. Sprinkle with remaining spice mixture, green onions, and chile peppers. Cook until onions and peppers just start to soften, 3 to 4 minutes.

Transfer potatoes to a plate and top with cilantro.