Tip flour into a large mixing bowl and stir in the mustard powder with the pinch of salt.
Make a well in the centre, crack in the egg, then pour in a dribble of milk.
Stir with a wooden spoon, gradually incorporating some of the flour, until you have a smooth batter in the well.
Now add a bit more milk and continue stirring until all the milk and flour has all been mixed together.
Set aside for half an hour
In the meantime preheat your oven to 220 degrees / gas mark 7 and add a large rectangular pan with the oil in the base and cook sausages and chopped onions for about 20 minutes until brown.
Turn sausages and return to oven for five minutes
Now this is the trick to a fine Yorkshire. That oil has to be the hottest thing on earth when you pour the batter in so I pull the oven shelf out and tip the batter in immediately. And then slam the door shut. You do not want the oil to cool down even a little bit by taking it out.
Cook for 40 minutes or until golden brown.
Recipe by Mummy Barrow at https://www.mummybarrow.com/toad-hole-can-raisesomedough/