Chop the onion and brown it in a large non-stick pan with some oil, then add the minced meat and let it flavour, then add the wine.
Season with salt, then transfer to a bowl and leave to cool.

Beat the egg lightly, then add half of it (keep the rest aside) to the now warm minced meat, together with the parmesan, and mix.

Unroll the puff pastry, place the molds on top (without pressing) and cut out circles slightly larger than the molds themselves.
Lightly butter the molds and line them with the puff pastry circles you just created, then prick the bottom with the tines of a fork.

Distribute the filling (minced meat and mozzarella cubes) into the puff pastry shells and, with the leftovers, create strips with which you will decorate the surface, creating a lozenge pattern.

Brush with the remaining egg and cook for about 20 minutes or until golden in a fan oven preheated to 180°C.

The tarts filled with meat and mozzarella are ready, let them cool slightly before serving.