Method

• 1.
  Preheat the oven to 180°C. Place cream, thyme, garlic and 2 tsp salt flakes in a large saucepan over medium heat and bring to just below the boil. Simmer for 5 minutes to infuse, then remove from heat.

• 2.
  Thinly slice celeriac (we used a mandoline) and layer into a 21cm gratin dish. Pour over the cream mixture and place dish on a baking tray. Cover with baking paper, then foil and bake for 1 hour or until celeriac is tender when pierced with the tip of a sharp knife. Remove from oven, uncover and scatter with Gruyere.
• 3.
  Return to oven for a further 40 minutes or until golden and bubbling.