Celeriac and Cyprus Potato Gratin | What Dad Cooked

Ingredients

• 750g Cyprus potatoes (or other waxy type)
• 500g celeriac
• 1 clove garlic
• 300 ml single cream
• 300 ml water
• 150 ml chicken stock or water
• 200g grated cheddar cheese (or Gruyere)
• 75g grated Parmesan cheese (or Gruyere)
• 4 bay leaves
• 1 sprig thyme
• Salt and pepper
• 50g softened unsalted butter
• 25g cold unsalted butter