Baked cod with white sauce

Ingredients

• 500 g cod fillet, skinned and boned
• 2 large carrots, sliced
• 2 leeks, sliced
• 1 bunch fresh parsley, roughly chopped
• 50 g plain flour
• 0.5 l full-fat milk
• 2 eggs
• 1 tbsp yellow mustard
• 1 tsp salt
• 6 turns of a pepper grinder