Peel the potatoes and slice them into waffle cuts using a mandoline with a waffle blade set to 0.25 inches, rotating the potato 90 degrees between each slice. Drop the pieces into a large bowl of cold ice water as you go.

Soak the sliced potatoes in the cold water for at least 30 minutes, then drain and pat completely dry with a kitchen towel or paper towels.

Heat the 1 qt vegetable oil in a large heavy pot to 300°F (150°C). Fry the potatoes in 2 to 3 batches for 4 to 5 minutes per batch until pale and just cooked through. Transfer to a wire rack and rest for 10 minutes.

Raise the oil to 375°F (190°C) and fry the potatoes again in batches for 3 to 4 minutes per batch until deeply golden and blistered at the edges.

Transfer each batch immediately to a wire rack or paper-towel-lined bowl. Sprinkle the 1.5 tsp kosher salt, 0.5 tsp garlic powder, and 0.25 tsp smoked paprika over the hot fries, toss to coat, then pile onto a serving plate and serve right away.