Preheat the oven to 200 ° C (top / bottom heat). Then grease a tart pan (approx. 26-28 cm).
Roll up the puff pastry and press it into the greased dish. Cut off the protruding edges a little. But there should be a margin.
Peel and thinly slice the sweet potatoes and carrots. Take the beetroot out of the pack and slice it thinly. Cut the shallots into rings or thin wedges. Then spread the vegetables on the puff pastry.
Mix the sour cream with the eggs and cheese and season well. Pluck the leaves from the thyme sprigs and add to the mixture. Then distribute everything over the vegetables.
Bake the tart in the preheated oven on the middle rack for about 20-25 minutes until the surface is golden brown.