Bring a large pot of generously salted water to a rolling boil. Add the penne and cook until just al dente, about 10 minutes. Before draining, scoop out and reserve 1/4 cup of the starchy pasta water, then drain the pasta.
Meanwhile, peel and devein the shrimp if necessary. Pat them dry and lightly season with salt and pepper.
Heat a skillet over medium-high heat and add a tablespoon of olive oil. Once shimmering, add the shrimp and sear for 2-3 minutes per side until pink, opaque, and slightly golden. Remove the shrimp from the skillet and set aside.
In the same skillet, add another splash of olive oil if needed, then toss in the crushed garlic. Cook gently for about 30 seconds until fragrant and just starting to turn golden—avoid burning it.
Add the cooked shrimp back to the skillet along with a splash of the reserved pasta water. Stir and simmer for about a minute, allowing the flavors to meld and the sauce to loosen.
Now, add the drained penne to the skillet, tossing vigorously to coat each piece with the sauce. Gradually pour in the remaining pasta water, a tablespoon at a time, until the sauce becomes silky and clings to the pasta—this should take about 2-3 minutes.
Squeeze fresh lemon juice over the pasta and sprinkle with chopped parsley. Toss again to distribute, watching for a bright aroma and glossy appearance.
Remove from heat and let rest for a minute to allow flavors to settle. Taste and adjust seasoning if needed—add a little more lemon or salt if desired.
Serve immediately while hot, garnished with extra parsley if desired, and enjoy the silky, flavorful shrimp penne.
