Batter can be made a day before.
Sift the flour and salt into a bowl.
In a separate bowl gently beat the eggs then add the milk and mix.
Pour into the flour, stirring continuously to create a smooth batter.
Rest in fridge until needed.
Preheat oven to 220°C.
Fry the sausages for 5 minutes until they start to colour, transfer to the individual roasting trays and heat the oil with sausages until very hot.
Pour in the batter mix until it's three quarters of the way up the sausages.
Place roasting tray in oven and bake for 35-40 minutes. Do not open oven door.
Peel the apples quarter and de-core. Roughly chop. In a saucepan heat half the butter and add the apples and sugar. Gently stew until you have an apple sauce consistency. Keep warm until needed.
Heat the remaining butter in a separate pan and gently fry the onions for around 20 minutes until caramelised but not burnt.
Spoon the apple sauce and then the onions onto the toad-in-the-hole and serve.
Serve with roasted onions and mashed potato.