Pat the shrimp completely dry with paper towels.
Melt 2 tablespoons of the butter in a 12-inch skillet over medium-high heat. Sear the shrimp in a single layer, working in batches if needed, about 90 seconds per side, until pink with slightly translucent centers. Remove to a plate.
In the same skillet, melt 1 tablespoon of butter over medium heat. Add the shallot and cook 2 minutes until translucent. Add the garlic and cook 30 seconds until fragrant.
Add the white wine and crushed red pepper flakes. Raise heat and simmer for about 8 minutes, until the liquid has reduced by half and coats the back of a spoon.
Lower heat to medium-low. Whisk in the remaining butter, a tablespoon or two at a time, letting each piece melt before adding the next, until the sauce is glossy and emulsified.
Return the shrimp to the skillet along with any juices. Toss gently and cook 1–2 minutes, until heated through and fully opaque.
Remove from heat. Stir in the lemon juice and parsley. Season with salt to taste. Serve immediately with toasted crusty bread.