Diana Henry's beef pie with wild mushrooms and red wine

1kg braising beef, cut into large chunks

30g dried wild mushrooms

Groundnut oil

350g baby onions, or small round shallots, peeled but left whole

50g butter

1 celery stick, finely chopped

2 garlic cloves, crushed

30g plain flour

300ml red wine

Leaves from 3 thyme sprigs

3 bay leaves

300g fresh mushrooms, sliced

3tbsp finely chopped flat leaf parsley leaves

320g puff pastry for 1 big pie, 600g for 6 small pies

1 egg, lightly beaten

Sea salt flakes and

freshly ground black pepper