Step 1

Heat the oven to 400°F/200°C. Toss the leeks and chopped parsnips with the olive oil in an 8-inch x 6-inch casserole or roasting pan (or a similar-sized round one). Sprinkle over half the thyme leaves and season well. Roast for 35 minutes or until the leeks are soft and buttery, and the parsnips are soft all the way through.

Step 2

Meanwhile, mix all but ½ cup/50 g of the grated parsnips in a bowl with the crème fraîche, chopped garlic, lemon zest, cider vinegar, stock and navy beans. Taste and season with salt and pepper, if needed.

Step 3

In a separate bowl, make the crumble topping. Using your fingertips, rub the oats, butter or olive oil, flour and pumpkin seeds together with the remaining grated parsnip and thyme leaves so that it starts to clump and looks like chunky breadcrumbs. Chill in the fridge until needed.

Step 4

Once the leeks and parsnips have softened, remove from the oven, toss through the bean and crème fraîche mixture, then tip back into the pan.

Step 5

Remove the crumble topping from the fridge, sprinkle it over the filling, sprinkle over the cheese and return to the oven for 30 minutes. Serve with warm, crusty bread and lemon-dressed salad or greens. Make Ahead: You can put the crumble together, cover and chill in the fridge up to 24 hours before you bake it.