Salmon in Vodka Cream Sauce with Green Peppercorns

8 tablespoons butter
1 onion, thinly sliced
1 pound spinach
6 6 ounce salmon fliets
salt and freshly ground pepper
3 tablespoons olive oil
1 1/2 cups whipping cream
1/2 cup vodka
2 tablespoons green peppercorns in water, drained and crushed
3 tablespoons fresh lime juice
1/4 cup snipped fresh chives

Preheat oven to 350F.  Combine 4 tablespoons butter and onion in large
Dutch oven.  Cover and bake until onion is golden brown, stirring
occasionally, about 45 minutes.

Stir spinach into onion and bake until just wilted, about 3 minutes. 
Remove from oven; keep warm.

Season salmon with salt and pepper.  Heat oil in heavy large skillet
over high heat.  Add salmon in batches and cook about 3 minutes per side
for medium.  Transfer to platter.  Tent with foil to keep warm.  Pour
off excess oil from skillet.  Add cream and vodka and boil until slightly
thickened, about 4 minutes.  Add green peppercorns and remaining 4
tablespoons butter and stir until butter is just melted.  Mix in lime
juice, season with salt and pepper.

Divide spinach and onion mixture among plates.  Top each with salmon
fillet.  Spoon sauce over.  Sprinkle with snipped fresh chives.