Scotch Beef and Haggis Pie

For the pie filling:

600g lean Scotch Beef, minced

454g good quality Haggis

1 large onion, finely diced

2 medium carrots, finely diced

1 stick celery, finely diced

2 tablespoons vegetable or Scottish rapeseed oil

135g pack of pancetta/lardon/bacon cubes

600ml beef stock (fresh or made with a stock cube)

1 tablespoon of red wine vinegar

1 teaspoon Worcestershire sauce

Pinch of salt and black pepper

2 tablespoons of flour to thicken

1 teaspoon of thyme (fresh or dried)

For the pie topping:

600g potatoes (Maris Piper or Desree varieties work well), peeled and chopped into equal sized chunks

300g swede, peeled and chopped into equal sized chunks

50ml milk

1 tablespoon butter

150g mature cheddar cheese (reserve a handful to scatter on top of the pie before baking)

1 teaspoon English mustard (optional)