For the onion tart, roll out the defrosted dough thinly and line a tart pan with it, also forming a rim about 2 cm high.
Prick the dough base several times with a fork and let it rest for a while. In the meantime, sauté the onion slices in butter until translucent and remove from heat.
Add grated cheese and beaten eggs and season with salt, pepper and paprika powder. Pour the warm mixture onto the pastry sheet and sprinkle the top with grated cheese.
Bake the onion tart in the oven over medium heat until golden brown.