Cook the pasta in boiling salted water as per the package directions; drain and set aside.Note: To use your time most efficiently, begin cooking the shrimp and sauce while waiting for the water to boil and the pasta to cook. By the time the pasta is cooked, the shrimp and sauce should be done or nearly done.
Lightly season the shrimp with salt and pepper.
Heat the olive oil and 1 tablespoon of the butter in a large skillet (I use a 12-inch skillet) over medium-low heat.
When the butter has melted, add the garlic and the crushed red pepper flakes (if using). Sauté, stirring constantly, just until the garlic is fragrant, about 1 minute.
Add the shrimp; sauté just until they are cooked through, about 1 to 2 minutes per side (they are done when they turn pink, firm, and opaque and curl up into a loose C shape). Be careful not to overcook, as they can become rubbery.Note: Do not allow the garlic to brown, as it will become bitter. You should be fine over medium-low heat, but since all stoves are different, just keep an eye on it and reduce the heat to low if necessary.
Remove the shrimp to a plate or bowl.
Add the wine and lemon juice to the pan. Increase the heat and bring to a gentle boil; allow to reduce for 3 minutes.
Reduce the heat to low. One tablespoon at a time, whisk in the remaining 4 tablespoons of cold butter, whisking constantly until each piece is melted before adding the next piece.
Return the cooked shrimp to the pan along with the cooked pasta and the parsley; toss until the pasta and shrimp are heated through and evenly coated with the sauce.
Taste and adjust seasoning, if needed. Serve immediately.