Whisk together the eggs, flour, goats’ milk, water and mustard and season with salt and milled pepper until you have the consistency of double cream without any lumps. Leave to rest for 15 minutes in a jug.
Cook the sausages in a little olive oil until nicely browned. Remove from the pan.
Add the onions and cook until browned and soft and do the same with the mushrooms.
Place the beef dripping into a medium sized roasting tray or a large ovenproof frying pan until smoking hot.
Remove from the oven and add the sausages, onion, mushrooms and rosemary. Pour over the batter and top with the goats’ cheese.
Bake until puffed up and golden in colour, 25 to 30 minutes.