In a large pot, bring salted water to a boil. Add the linguine or spaghetti and cook according to package instructions until al dente. Drain and set aside, reserving 1/2 cup of the pasta water.
In a large skillet over medium heat, melt 4 tablespoons of butter. Add the minced garlic and red pepper flakes, sauté for about 1 minute until fragrant.
Increase the heat to medium-high. Add the shrimp to the skillet, season with salt and pepper, and cook until they turn pink (about 2-3 minutes on each side).
Once the shrimp are cooked, pour in the lemon juice and zest; add the remaining 2 tablespoons of butter and toss until melted. If the sauce seems too thick, stir in some reserved pasta water to reach desired consistency.
Add the cooked pasta to the skillet with the shrimp, tossing everything together to combine well. Adjust seasoning if necessary.
Remove from heat, sprinkle with fresh parsley, and serve hot. For extra flavor, top with grated Parmesan cheese if desired.
Notes
For extra flavor, top with grated Parmesan cheese if desired.