1Cut the russet potato into 1/4-inch fries. Rinse under cold water until the water runs mostly clear, then soak in cold water for at least 30 minutes.
2Drain the fries and dry them very thoroughly with clean towels. Any remaining water can cause the oil to splatter.
3Heat 2 to 3 inches of peanut oil in a heavy pot to 325°F.
4Fry the potatoes in batches for 4 to 5 minutes, until tender and pale but not browned. Transfer to a rack or paper towels and let them rest for at least 10 minutes.
5Raise the oil temperature to 375°F. Fry the potatoes again in batches for 2 to 4 minutes, until deeply golden and crisp.
6While the fries are hot, toss them with the garlic, Parmesan, kosher salt, and parsley if using. Serve immediately.
For a gentler garlic flavor, briefly sauté the minced garlic in 1 teaspoon of the hot frying oil before tossing it with the fries.
Do not add the garlic before frying; it will burn in the oil.
Use a thermometer if possible, and add the potatoes gradually so the oil temperature does not drop too far.