Add flour into the large mixing bowl and stir in the mustard powder with a good pinch of salt.
Make a well in the centre, crack in the egg, then pour in a little milk. Stir with a wooden spoon, gradually incorporating some of the flour, until you have a smooth batter in the well.
Add a bit more milk and continue stirring until all the milk and flour has been mixed together.
Pour the batter into a jug and set aside.
Add the sausages and 1 tbsp of the oil to the baking dish and roast in the hot oven for 15 minutes.
Take the hot tray from the oven, then quickly pour in the batter – it should sizzle and bubble a little when it first hits the hot fat.
Put it back into the oven, then bake for 40 mins until the batter is cooked through, well risen and crisp.
Poke the tip of a knife to the centre to check if it is set and not runny
Gravy
Soften the onions in the oils and cook for 15 minutes.
Add a teaspoon of flour and stir constantly to thicken. Add the brown sugar
Gradually pour in the stock and let it all bubble together for 5 minutes
Cut the Toad in the hole into slices and serve hot with gravy