I start by peeling the russet potatoes and slicing them into fry-shaped sticks, about a quarter-inch thick so they cook evenly. As soon as they're cut, I drop them straight into a bowl of cold water. This keeps them from browning while I get everything else ready, and it also pulls out a little extra starch for a crisper finish.
While the potatoes are soaking, I sift the flour together with the garlic salt, onion salt, plain salt, and paprika in a mixing bowl. Then I gradually stir in the water, just enough that the batter is loose enough to drizzle off a spoon. This seasoned batter is what gives these fries their crunchy, flavorful shell once they hit the hot oil.
I heat the vegetable oil in a large skillet over medium-high heat while I finish the batter. Getting the temperature right matters here, since fries dropped into oil that isn't hot enough will turn out greasy instead of crisp. I usually test with one potato stick first to see if it sizzles right away.
I drain the potato sticks and pat them mostly dry, then dip each one into the batter before placing it into the hot oil. I add them one at a time so they don't clump together, working in small batches. I let them fry until they're deeply golden and crisp on the outside, which usually takes just a few minutes per batch.
Once they're golden brown, I lift the fries out with a slotted spoon and set them on paper towels to drain any extra oil. I give them a final light sprinkle of salt while they're still hot, since seasoning sticks best right out of the fryer. From there, they're ready to serve immediately while they're at their crispiest.