Next level sausage rolls

Name: Next level sausage rolls
Prep time: 1 h
Cook time: 35 min
Total time: 1 h 35 min
Cuisine: European, British
Ingredients: 800g Morrisons Butcher's Style Pork Sausagemeat; 100g sage & onion stuffing mixture; 1 egg beaten; English mustard ketchup or brown sauce, to serve; 250g pack butter frozen; 400g plain flour (or 350g plain flour and 50g white rye flour), plus extra for dusting; 1 tsp English mustard powder; 1 tbsp cider or white wine vinegar