Preheat the oven to Gas mark 5, 190°C, fan 170°C. Lightly grease 6 small gratin or ramekin dishes.
Cut carrots, celeriac, parsnip and sweet potato into 1½cm (¾in) cubes.
Half fill a saucepan with water and bring to the boil. Add vegetables and cook for about 5 minutes, or until just tender. Drain, reserving the cooking liquid. Then set the vegetables aside.
Melt half the butter in a saucepan over medium-high heat. Add the bay leaf and pancetta and cook for a few minutes, or until pancetta is starting to brown lightly. Add spring onion whites and cook for 3 minutes or until softened, then remove mixture from pan and set aside with the vegetables.
Melt the remainder of the butter in the pan and add the flour, stirring well to combine. Gradually add 175ml (6fl oz) of the reserved vegetable cooking liquid, stirring until smooth.
Carefully stir in the crème fraîche until smooth, then add garlic and nutmeg. Add vegetable mixture and spring onion greens and mix well. Divide the mixture between the prepared dishes.
To make the crumble topping, rub butter into flour with your fingertips until the mixture resembles breadcrumbs. Stir in the ground almonds, Parmesan and rosemary.
Divide the topping evenly over the vegetables and cook in the oven for 25 minutes, or until golden. Serve with a green salad.
Inspired by her travels across the snow-cloaked regions of Europe, Jane Lawson's Snowflakes And Schnapps is a collection of hearty seasonal recipes and dinner-party treats. Published by Murdoch Books, £25, it's available online from www.tesco.com/books