Braise mushrooms in butter till nicely browned up, add capsicum and toss, remove on a platter.
In same pan add little oil and keep on flame add onions and 1 tsp sugar, caramalise the onions till browned up.
Remove on same platter let it cool down then toss all with mozarella cheese, salt and pepper and keep aside.
Cut puff pastry in squares and roll slightly press in centre with yor thumb, brush with beaten egg and bake on 200 degree C till creamish brown colour.