No Nightmare Beef Wellington

Name: No Nightmare Beef Wellington
Ingredients: 1 cup balsamic vinegar; 1 cup dry red wine; 1/2 cup sugar; 1 1/2 pounds sliced button mushrooms; 3 tablespoons butter, divided; 1/4 cup duck or goose liver pâté; 1 tablespoon chopped fresh thyme plus 6 sprigs for garnish; 6 frozen puff pastry shells (one 10-ounce package); 1 tablespoon canola oil; 6 4-ounce filet mignon steaks; Coarse kosher salt; 2 5-ounce bags fresh baby spinach; Balsamic Roasted Vegetables; Creamed Onions with Bacon and Herbs