Preheat oven to 425°. Fill a large bowl halfway with water. Cut potatoes into long slices about 1/4 in. thick, then cut in 1/4-in.-thick sticks, dropping them into water as cut. Drain and pat very dry.
Line 2 large rimmed pans with parchment paper. Put 1/2 of potatoes in each pan. Pour oil evenly over potatoes and mix to coat. Arrange potatoes in a single layer.
Bake potatoes for 20 minutes, then turn over with a wide spatula. Continue to bake potatoes, turning every 10 minutes, until crisp and deep golden, 20 to 25 minutes more.
In a large bowl, combine garlic, parsley, and butter. Add potatoes, mix well, and season to taste with salt. Serve immediately.
Note: Nutritional analysis is per 1-cup serving.