Spread the butter in a baking pan.
Lay the pastry in the baking pan, so as it exceeds a little bit at the edges, and open a few holes with a fork.
Bake at 160°C with extra heat on the oven elements, for approx. 20 min.
Cut the pancetta in small cubes and add them to the frying pan over low heat and saute.
Once the pancetta becomes crunchy, add the onion, in very thin slices.
Cut the garlic in very thin slices and dissolve it with a little salt, creating a paste. Add it to the frying pan. Stir.
Add the spinach and creme fraiche.
Add the cheese and lime zest.
Stir and add the eggs and yolks. Stir well again.
Take the pastry out of the oven and cut the edges.
Spread the stuffing and sprinkle with a little more cheese.
Bake at 160°C with extra heat on the oven elements, for approx. 30 min.
Leave it to cool down and serve.