Sausage and Mash Pie

Name: Sausage and Mash Pie
Prep time: 15 min
Cook time: 50 min
Total time: 1 h 5 min
Cuisine: British
Ingredients: 28oz / 800g Pork Sausages ((approx 12)); 3 cups / 750ml Beef Stock; 1/2 cup / 125ml Red Wine ((see notes)); 14oz / 400g Onion; 4 tbsp Plain Flour; 3 tbsp Butter; 2 tbsp Worcestershire Sauce; 1/4 - 1/2 tsp Dried Thyme; Salt & Black Pepper, (to taste); Olive Oil, (as needed); 4.4lb / 2kg White Potatoes, (peeled & diced into chunks (i.e Maris Pipers)); 1.5 cups / 150g Cheddar, (grated); 1/2 cup / 125ml Milk or Cream; 4 tbsp Butter; 1 heaped tbsp Dijon Mustard ((can reduce slightly if you're not keen on mustard)); Salt & Black Pepper (to taste)