Fluffy Chow Mug

Name: British Cornish Pasty-A Twist for Cornish Pasty Week
Ingredients: 300 g plain flour; 150 g unsalted butter (cold, diced); 1/2 tsp salt; 4–5 tbsp cold water; 250 g beef skirt (finely diced); 1 medium potato (peeled & diced); 1 small swede (peeled & diced); 1 small onion (finely chopped); Salt & black pepper (to taste); 1 tbsp butter; 1 egg (for sealing & glazing); 1 tbsp vegetable oil; 50 ml water