Preheat the oven to 220°C/425°F/Gas Mark 7
Place the sausages in a large metal roasting tin, spaced apart. Drizzle with the rapeseed oil and bake for 10 – 15 minutes until the sausages are starting to colour.
To make the batter, sift the flour and mustard powder into a bowl, make a well in the centre, beat the eggs with the milk and half of the water, tip the mixture into the well and incorporate the flour into the liquid and beat until you have a smooth batter. Season the batter with sea salt and black pepper, place the bowl in the fridge for at least 30 minutes, the batter can be made in advance.
Remove the sausages from the oven and if they haven’t released much fat, add another 1 – 2 tbsp of oil to the tray. Take the batter out of the fridge and add the remaining 55ml cold water, whisk well. Place the roasting tin on a direct heat and get the oil and the roasting tray very hot. Add the batter and place in the hot oven on the highest shelf and cook for a further 35 – 40 minutes, until the toad is fully risen and golden.