Green Bean Casserole

Ingredients

• 425ml milk
• 1 small onion, peeled and halved
• 2 bay leaves
• 2 cloves garlic, crushed
• 4 black peppercorns
• 600g green beans, trimmed and strung
• 300g chestnut cap mushrooms, sliced
• 40g unsalted butter
• 25g plain flour
• 1 egg yolk
• Juice of 1 lemon
• salt and pepper to taste
• 200g sour cream
• 2 tbsp. French’s® Classic Yellow Mustard
• 2 (79g) packets French’s® Crispy Onions