Preparing a Celeriac and Sweet Potato Bake

• 550g celeriac, medium sized or half a big one, 
• 550g sweet potatoes, peeled and then cut into inch size or roughly 2cm pieces
• 1 white onion, finely sliced
• 50g salted butter or unsalted butter but you may need extra seasoning, melted with some extra for greasing a baking dish
• 250ml double or heavy cream
• 100ml milk
• 1 tbsp. wholegrain or Dijon mustard
• 1½ fresh thyme leaves
• 80g white breadcrumbs – really fresh.

Preparation:

1. Preheat oven to 190°C (170°C fan) mark 5.
2. Place the celeriac and sweet potato pieces into a large saucepan and cover with cold water and a lid. Boil on a rapid high heat then simmer, uncovered, for 4 to 5 minutes, until both vegetables are tender. The celeriac is often the one to check here.
3. Add the sliced onion and cook for about a minute, then drain all the vegetables really well.
4. Grease a 3 litre ovenproof serving dish or roasting tin with butter. Whisk the cream, milk, whatever  mustard you have, a tablespoon of thyme and plenty of seasoning especially salt if unsalted butter is used.
5. Put all the drained vegetables into the ovenproof dish/roasting tin and pour over the herby-cream mixture. Try to mix the vegetables in as well as possible. 
6. Mix the fresh breadcrumbs with the melted butter. Add what’s left of the thyme and add some black pepper/salt to season. Sprinkle this crumb onto the vegetables.
7. Cook in the oven for between at least 40 minutes, you see it browning with a gold top. It should also be bubbling but take out if this it too violent.
8. Serve next to the roast meats although your guests may well have their own ideas.