In a large frying pan heat 1 tablespoon of rapeseed oil and the pancetta over a medium heat for 2 minutes.
Add the chopped chestnuts and cook for 1 minute.
Add the shredded brussels sprouts and coat in the pancetta oil and chopped chestnuts and turn the heat up to high.
Fry the mixture for a few minutes stirring occasionally.
When you see some caramelisation on the sprouts add a few tablespoons of water to get some steam going.
After another minute or so add the zest and juice of half the lemon and stir in.
Next add 2 - 3 tablespoons of crème fraiche, stir through and after 1 minute turn the heat off.
Taste and then season with salt and pepper.
Put the mixture in a serving bowl and squeeze the other half of the lemon over the top.
Finally, grate the other half of the lemon zest over the mixture and then serve immediately.