Peel onions, chopped them, then fry in oil, and cool down. Slice mushrooms, fry in one tablespoon of oil, then set aside to cool. Remove the puff pastry from the refrigerator, roll out and cut into half (along the long side). Remove the pâté from the aluminium moulds.
Put fried mushrooms in the middle of the pastry, then put some onions on the mushrooms. Put pâté and then mushrooms and onions. Cover the components with pastry strips with incisions. Spread mixed egg on top.
Prepare all four pieces of pâté the same way. Put them on a baking mould and place in an oven heated to 180°C with top and bottom heaters and the fan on. Bake until the cake is nice and brown (approx. 30 minutes).