Place the flour in mixing bowl, make a well in the centre and pour in beaten eggs with a little milk. Stir, gradually bringing flour into the centre and adding the remaining milk as you go, until you have a smooth batter. Set aside for 2 hours to rest.
Preheat the oven to 170ºC
For the filling:
Heat the olive oil in a large non-stick frying pan over a medium heat.
Add the sausages and cook until brown on all sides.
Pour any fat from the pan into a roasting tin, place the sausages on a rack over the tin and cook in the oven for 10 minutes.
Take the rack and sausages off the roasting tin, increase the oven temperature to 200ºC.
Lay the tomato and mushroom slices in the roasting tin and cook for 5 minutes.
Add the chopped parsley to the batter mix. Put the sausages on top of the mushroom and tomato slices and pour over the batter.
Return to the oven and cook for 30-40 minutes until the batter is well risen and golden.