Pat the shrimp thoroughly dry with paper towels: Season them evenly with 1/2 teaspoon salt and the black pepper. Keep them refrigerated while the pasta water comes to a boil.

Bring a 5- to 6-quart pot of water to a rolling boil. Add 1 tablespoon salt, followed by the linguine. Cook according to the package directions until just al dente, generally 9 to 11 minutes.

Before draining the linguine, scoop out 3/4 cup (180 ml) of the starchy cooking water. Drain the pasta without rinsing it.

While the pasta cooks, heat 1 tablespoon (15 ml) olive oil and 1 tablespoon (14 g) butter in a 12-inch skillet over medium-high heat. The butter should foam without becoming dark brown.

Add half of the shrimp in a single layer. Cook for 1 to 2 minutes, until the undersides are lightly golden and the edges begin turning opaque.

Turn the shrimp and cook for another 1 to 2 minutes. Transfer them to a clean plate when they are opaque and reach 145°F (63°C). Repeat with the remaining tablespoon of olive oil and remaining shrimp.

Let the cooked shrimp stand while preparing the sauce. They will be returned to the skillet only briefly, which helps prevent a rubbery texture.

Reduce the skillet heat to medium-low: Add 3 tablespoons (42 g) of the butter. Once melted, stir in the garlic and optional red pepper flakes. Cook for 30 to 45 seconds, until fragrant but not browned.

Add the lemon zest, 2 tablespoons (30 ml) of the lemon juice, and 1/2 cup (120 ml) of the reserved pasta water. Scrape the bottom of the skillet to loosen the browned shrimp bits.

Bring the liquid to a gentle simmer and cook for 1 to 2 minutes. Add the remaining 2 tablespoons (28 g) butter one piece at a time, stirring until each piece melts. The sauce should look glossy and lightly thickened rather than oily.

Add the drained linguine to the skillet: Toss continuously with tongs over low heat for 1 to 2 minutes, until the noodles are evenly coated. Add more reserved pasta water a few tablespoons at a time if the pasta looks dry or sticky.

Add the cooked shrimp and any juices from the plate. Toss gently over low heat for about 1 minute, just until the shrimp are warmed through.

Remove the skillet from the heat: Add the remaining 2 tablespoons (30 ml) lemon juice and the chopped parsley. Toss well. The sauce should cling lightly to the pasta with no large pool of butter beneath it.

Let the pasta stand for 2 to 3 minutes, then toss again. Divide among six plates and serve with lemon wedges and additional red pepper flakes as desired.