Shrimp Scampi

2 pounds jumbo shrimp, shelled and deveined
Salt and freshly ground black pepper
2 tablespoons unsalted butter
1 small onion, sliced thinly
2 tablespoons chopped garlic
1 lemon, juiced
1/2 cup white wine
2 tablespoons cold butter
1/4 teaspoon grated lemon zest
2 tablespoons chopped parsley leaves
Lemon slices, for garnish

1. Season the shrimp thoroughly with salt and pepper. Set aside for 10-15 minutes.
2. Heat a large skillet over medium heat. When the skillet is hot, add enough butter to lightly coat the skillet. Add the shrimp and quickly saute until just starting to turn pink, but not cooked through. Remove from the skillet and set aside.
3.Return the skillet to the heat and melt the rest of the butter. Add the onions and saute until just they begin to soften, about 3 minutes. Add the garlic and cook another 1 minute. Add the white wine and lemon juice. Boil the liquid until slightly thickened, about 3 - 4 minutes.
4. Add the shrimp back to the skillet. Mix well.
5. Stir in the zest and parsley.
6. Served with angel hair pasta or steamed white rice.