Ingredients

• 3 ounces (85 grams) chopped onions
• 1 ounce of butter
• 1.5 pounds (680 grams) lean minced beef
• 1.5 teaspoons salt
• 1/8 teaspoon pepper
• Fresh thyme
• 1 egg
• 1 ounce softened butter or pork fat
• For stuffed mushrooms
• 6 large mushroom caps
• 1/2 ounce (16 grams) Parmesan cheese
• 1/2 ounce Gruyere cheese
• 1.5 tablespoons plain white bread crumbs
• 2 tablespoons chopped parsley
• 3 tablespoons chopped onion
• 3 tablespoons chopped spring onion or shallot
• Salt and pepper to taste
• Dried tarragon
• Heavy cream
• Melted butter