Salmon Wellington

Ingredients

• 8 (6 oz.) salmon fillets, cut about 3/4 inch thick
• 1 egg yolk mixed with 1 Tbsp. milk for glaze
• 1 pkg. puff pastry
• 3 Tbsp. butter or margarine
• salt and pepper
• 1 lb. mushrooms, coarsely chopped
• 2 onions, chopped
• 6 Tbsp. dry white wine
• 6 Tbsp. white wine vinegar
• 2 Tbsp. finely chopped shallots
• 1 1/2 c. whipping cream, at room temperature
• 1 tsp. salt
• white pepper
• 2 Tbsp. finely chopped chives or parsley