Bring a pot of water to a boil, add the spaghetti and cook until al dente.

In a large skillet, melt 1 tablespoon of butter over medium heat. Add the shrimp to the pan in a single layer and cook until they turn opaque, about 1-2 minutes per side. Depending on the size of the pan the shrimp may need to be cooked in batches. Once cooked remove from the pan and set aside.

Next, add 2 tablespoons butter to the pan. Once melted, add the garlic (and red pepper flakes, if using) and cook until the garlic is softened. Lower the heat, if necessary, to avoid browning the garlic.

Add the wine, zest, and lemon juice. Bring to a boil and allow the mixture to reduce for a minute or so. Lower the heat and whisk in the rest of the butter (1-2 tablespoons at a time). 

Add the cooked shrimp to the sauce and toss to coat. Sprinkle the parsley over the top. Add in the cooked spaghetti and, using tongs, toss everything together. Serve with lemon wedges on the side.