Beef medallions with a chestnut crust

Ingredients

• 100 g frozen peeled chestnuts
• 4 sprigs rosemary
• 25 g butter
• ¼ tsp sea salt
• a little pepper
• 40 g grated Parmesan
• 1 onion
• 1 garlic clove
• 600 g savoy cabbage
• 1 pear
• 1 tbsp butter
• 1 bay leaf
• 1 dl white wine
• 1 dl vegetable bouillon
• 200 g crème fraîche
• ¼ tsp nutmeg
• salt
• pepper
• a little clarified butter
• 4 beef fillet medallions
• ½ tsp salt
• 40 g Parmesan