Preheat the oven to 180°C, fan 160°C, gas mark 4.
Heat the tomatoes in a pan with the vegetable stock. Simmer for 10 minutes and season with salt, pepper and sugar to taste.
Layer the drained artichokes and the sweet potatoes in an ovenproof dish. Stir the crème fraîche into the tomato sauce, then pour over the veg.
Mix the grated cheese with the breadcrumbs and fresh thyme, then scatter this over the veg.
Bake in the preheated oven for 40 minutes, then cover with foil and bake for a further 20 minutes, until the potatoes are tender.
* Please note, this recipe is not suitable for vegetarians as it contains Gruyère.