Preheat the oven to 220°C, gas mark 7. Twist each chipolata in the middle, and cut into two small sausages. Stretch the rashers of bacon out with the flat of a knife and cut each into three slices. Wrap each sausage in a piece of bacon. Take a 12-hole muffin tray and drizzle a little oil into the base of each hole. Then divide the sliced leek between the holes, and top with two of the little bacon-wrapped sausages. Cook in the hot oven for 12-15 minutes until just starting to brown.
While the sausages are cooking, sift the flour into a bowl and season. Whisk in the eggs and milk to make a smooth batter. Take the sausages out of the oven and pour the batter over them, then drop a little of the onion marmalade into the centre of each little toad hole.
Return to the oven for a further 20-25 minutes until the batter is puffy, crisp and golden, and the sausages are browned and cooked through. Serve with creamy mashed potato, steamed green beans and, if you wish, an extra spoonful of onion marmalade.