Peel and roughly chop the onions and carrots, and peel and chop the potatoes into 2cm chunks. Trim, halve and wash the leeks, then finely slice. Roughly chop the bacon. Chop all the chicken meat into 3cm chunks
Tie the herb sprigs together with string to make a bouquet garni.
Heat 1 tablespoon of oil in a large pan on a medium heat, add the chicken and bacon, then cook for a few minutes, or until lightly golden. Add the onion, carrot potatoes and leeks, then cook for a further 15 minutes, or until softened , stirring occasionally.
Next, add a knob of butter, then stir through the flour to coat.
Gradually pour the chicken stock into the pan, then stir in the English mustard, creme fraiche, and the bouquet garni, and continue cooking for 10 minutes, stirring regularly. Season with white pepper.
Meanwhile, make your pastry. Chop the butter into cubes, then put into a bowl with the flour, suet and a good pinch of salt. Use your thumbs and forefingers to rub the butter into the flour until it resembles cornflake shapes.
Lightly stir in 100ml of cold water, then use your hands to gently pat and push together into a rough dough. Do not overwork it. Wrap the dough in clingfilm and put in the fridge until needed.
Meanwhile, for the meatballs, pick and finely chop the sage, season with salt and pepper, then using you hands, scrunch and mix with the veal. Roll into 3cm balls, then gently place into a large pan with a splash of oil and cook for 10 minutes, or until golden.
Add the filling to a large oval pie dish (roughly 25cm x 30cm), discarding the bouquet garni, then leave to cool slightly, then dot the balls on top.
Roll out the pastry on a flour-dusted surface so it’s slightly bigger than your pie dish. Beat the egg, then brush over the edge of the pie dish, drape over the pastry, press lightly to stick, then trim away the excess, pinching or crimping with a fork to seal.
Eggwash the top, then use the excess pastry to decorate the top of the pie, if you like.
Bake in the oven for around 50 minutes, or until golden, then leave to stand for 10 minutes before serving with some steamed, seasonal greens.