To make the Yorkshire puddings, sift the flour and salt into a large bowl and mix in the eggs and half the milk. Whisk until a paste, then add the other half of the milk and whisk until smooth. Rest for 30 minutes.
Preheat oven to 220°C (425°F)
Add a teaspoon of vegetable oil to each muffin tin hole and heat until sizzling. Turn the oven down to 200°C (400°F) and pour a tablespoon of Yorkshire pudding batter into each hole. Bake for 15 minutes or until risen and golden brown.
To make the mash, peel and slice three medium potatoes. Boil in salted water until soft. Drain, then add the butter, sour cream, and milk, and mash until smooth. Season with salt, pepper, and fresh chives.
To make the bangers, quarter two sausages and chop one onion. Fry the onion for two minutes, then add the sausages and fry both until cooked.
To assemble, add a teaspoon of gravy to the bottom of the Yorkshire pudding, then add the onions on top, then the mash and a sausage quarter. Sprinkle with more chives.