Baked Eggs and Mushrooms in Ham Crisps

INGREDIENTS

• 3/4 lb mushrooms, finely chopped
• 1/2 teaspoon salt
• 1 tablespoon finely chopped fresh tarragon
• 2 tablespoons unsalted butter
• 12 large eggs
• 1/4 cup finely chopped shallot
• Garnish: fresh tarragon leaves
• 1/4 teaspoon black pepper
• 2 tablespoons crème fraîche or sour cream
• 12 slices Black Forest or Virginia ham (without holes; 10 oz)
• Accompaniment: buttered brioche or challah toast