Step #2 Pour the sunflower oil into a solid based 9 inch by 6 inch baking tray.
Step #3 Throw in the cut up onion & scatter in the sausages.
Step #4 Place in the hot oven, on the lowest shelf, for about 15 mins while you make the batter.
Step #5 Using a sieve & holding it up high above the bowl sieve the flour into the bowl.
Step #6 (Doing this from a height forces air into the flour & gives you a lighter batter.
Step #7 Make a well in the middle of the flour & using a whisk, whisk in the egg & milk, along with some salt & pepper.
Step #8 As you whisk the flour will be incorporated from the edges & you will end up with a nice lovely thick & smooth batter.
Step #9 Whisk in the grainy mustard.
Step #10 Take the hot pan of sausages out of the oven & quickly pour the batter in & around the sausages while the fat in the pan is still sizzling.
Step #11 Return the pan to the oven, placing it on the highest shelf this time, & continue to bake for 30 mins longer, until the sausages are nicely browned & the batter has puffed up all nice & brown around them.