Heat the oven to 425°F and line a sheet pan with parchment paper.

Soak the potatoes in cold water 15 minutes, drain, and pat completely dry.

Toss with oil, cornstarch and salt, spread in a single layer, and bake 35 to 40 minutes, flipping once, until deep golden and crisp.

While the fries finish baking, warm the melted butter and garlic together in a small pan over low heat for 1 minute, just until fragrant, watching closely so the garlic does not brown.

Transfer the hot fries straight into a large bowl and pour the garlic butter over them.

Toss well to coat every fry, then add the parmesan and toss again.

Pile onto a platter, finish with parsley and red pepper flakes if using, and serve immediately while the cheese is still melting into the fries.