Dissolve yeast extract in the 285 ml / 1 1/3 cup / 10 fl oz warm water.

Place the tofu slices in a shallow bowl and pour the yeast extract liquid over them. Leave to marinate for an hour or two. Turning the slices occasionally if possible.

Combine the 55 g / 2 oz / 1/2 cup flour with the paprika, oregano, and a t of pepper and spread out on a plate.

Lift each tofu slice from the marinade, gently squeezing the marinade from it back into the bowl, and coat both sides with the flour. Saute in 2 T of the vegetable oil in a frying pan, turning once, until light browned on both sides. Set aside.

Chop the onions and saute in a saucepan the remaining oil for 2-3 minutes. Peel and chop the tomatoes. Chop the celery and mushrooms finely. Add to the saucepan.

Add the yeast extract marinade to the saucepan, bring to the boil, cover and simmer for about 3 minutes.

Combine 2 T flour with 2 T water in a cup. Stir this into the vegetable mixture until thickened.

Place tofu slices at the bottom of an oiled casserole. Pour the vegetable mixture over them. Bake at 350F/180C for about half an hour.