For the pancakes

• 100g (3½oz) buckwheat flour
• Good pinch of fine sea salt
• 1 egg
• 150ml (5fl oz) whole milk
• 1 knob of unsalted butter

For the filling

• 400g (14oz) bright-purple sprouting broccoli
• ½ celeriac, peeled and cut into 1–2cm (½–¾in) pieces
• 1 onion, halved and sliced
• 200g (7oz) firm chestnut mushrooms, thickly sliced
• 4 garlic cloves, thinly sliced
• ½ small handful of thyme
• 2 tbsp extra-virgin olive oil
• 1 tbsp buckwheat groats (optional)
• Sea salt and freshly ground black pepper

For the white sauce

• 1 litre (35fl oz) whole milk
• 4 bay leaves
• 1 onion, sliced
• 1 celery stick, sliced
• A few black peppercorns
• 70g (2½oz) unsalted butter
• 70g (2½oz) plain flour
• 150g (5½oz) hard sheep’s or cow’s cheese, grated

Heat the oven to 200°C/180°C fan/400°F/gas mark 6.

Make the pancake batter. Place the flour and salt in a large bowl. Make
a well in the centre and crack in the egg. Combine the milk with 150ml (5fl oz) of water. Pour half the milk and water mixture into the bowl and whisk until you have a thick, smooth batter. Pour in the remaining milk and water mixture and whisk again. You’re aiming for the consistency of double cream. Cover the batter and refrigerate until needed.

Start the filling. Bring a pan of salted water to the boil. Add the purple sprouting broccoli, bring back to the simmer and cook for 3–4 minutes, until just tender, then drain and set aside.

Scatter the celeriac, onion and mushrooms out over a large baking tray and add the garlic. Strip the leaves from half the thyme and add these, too, then trickle over the olive oil. Season well with salt and pepper and tumble everything together. Place the baking tray in the hot oven and roast, turning the vegetables occasionally, for 35–40 minutes, until all lovely and tender. Transfer the roasted vegetables to a large mixing bowl.

While the vegetables are roasting, heat the milk for the white sauce with the bay leaves, onion, celery and peppercorns. When it begins to simmer, remove the pan from the heat and set aside to infuse.

When you’re ready to cook the pancakes, heat a large non-stick frying
pan over a low heat. Add the knob of butter and, when it’s bubbling,
pour nearly all of it into the bowl of batter and whisk. Add a small ladleful of the pancake batter to the pan, then tilt the pan to spread the mixture out evenly.

As it sets, after about 1 minute, lift up the edge of the pancake with a spatula, then flip the pancake over. Cook the other side for 30–40 seconds, until golden, then slide the pancake out onto a warm plate. Repeat until you’ve made 6 pancakes in total.

Heat the butter for the white sauce in a medium, heavy-based pan over
a medium heat. Scatter over the flour and, using a wooden spoon, work
it into the butter. Cook gently, stirring regularly, for 1 minute. Set a sieve over the pan and pour in half the infused milk. Remove the sieve and work the milk into the butter and flour mixture. Once it thickens, replace the sieve and pour in the remaining milk, then remove the sieve again and beat the sauce with a whisk to a thick, smooth consistency. Add half the grated sheep’s cheese and season with plenty of salt and pepper. Stir well.

Pour half the sauce into the celeriac and mushroom mixture and stir well. Season the mixture with salt and pepper.

Lay out your pancakes on a large, clean work surface. Divide the broccoli between them, then spoon over equal amounts of the celeriac and mushroom mixture. Carefully roll up the pancakes and place them in a large baking dish side by side. Pour over the remaining white sauce and scatter over the remaining cheese, the buckwheat groats (if using) and the remaining thyme sprigs.

Bake in the oven for 25 minutes, or until golden brown on top and bubbling. Serve with a dressed green salad.