Heat your oven to 200°C/Fan 180°C/Gas 6. Trim the ends off the leeks and carrot and thickly slice. Crumble the stock cube into a heatproof jug and pour in 400ml boiling water. Stir to dissolve.
Heat 1 tbsp oil in a heavy based pan. Cook the chicken for 4-5 mins to brown on all sides. Lift out of the pan with a slotted spoon and place in a bowl.
Tip the chopped veg into the pan and fry on a low heat for 5 mins. Return the chicken to the pan along with any juices. Pour in the chicken stock and add half the thyme leaves. Cover and simmer for 10 mins.
Meanwhile, peel and coarsely grate the parsnips into a large bowl. Add the flour, the remaining thyme leaves and a pinch of salt. Beat the egg in a small bowl with 1 heaped tbsp crème fraîche. Pour into the parsnip and flour. Mix together to form a soft, sticky dough.
Zest and juice the lemon. Add to the remaining crème fraîche. Pour into the simmering chicken and stir to combine. Taste and season with salt and pepper. Transfer the mix to an ovenproof dish.
Pull golf ball sized pieces off the dough – they don’t need to look too neat. Drop them on top of the creamy chicken – they should half float.
Bake in the oven for 20 mins. The top of the cobbler should be golden brown and set, and the chicken stew bubbling. Serve in warm bowls.