Step 1: Cook the pasta. Bring a large pot of heavily salted water to a rolling boil. Add the pasta and cook according to package directions until al dente. Before draining, reserve about 1 cup of the starchy pasta water. Drain the pasta and set aside; do not rinse.
Step 2: Sauté the shrimp. While the pasta cooks, melt 2 tablespoons of butter in a large skillet or Dutch oven over medium-high heat. Add the shrimp in a single layer, season with salt and pepper, and cook for 1-2 minutes per side until pink and opaque. Do not overcrowd the pan; cook in batches if necessary. Remove the cooked shrimp to a plate and set aside.
Step 3: Build the garlic cream sauce. Reduce the heat to medium. Add the remaining 2 tablespoons of butter to the same skillet. Add the minced garlic and cook for about 1 minute, stirring constantly, until fragrant. Be careful not to burn it. Pour in the heavy cream and bring it to a gentle simmer, stirring occasionally. Let it cook for 2-3 minutes, allowing it to thicken slightly. Season with salt, black pepper, and red pepper flakes (if using).
Step 4: Combine and serve. Add the cooked pasta to the skillet with the cream sauce. Toss to coat evenly. Stir in the Parmesan cheese until melted and smooth. If the sauce is too thick, add a splash of reserved pasta water, a tablespoon at a time, until it reaches your desired consistency. Gently fold in the cooked shrimp and fresh parsley. Serve immediately, garnished with extra Parmesan and a fresh lemon wedge.