Peel and dice the carrots and onions. Peel and dice the potatoes (put in water); quarter the mushrooms and dice the celery.
Place the meat in a deep tin. Add the carrots, onions, mushrooms and tomato base sauce. Add a little water to thin the sauce and cook in the preheated oven for 1.5-2 hours. The meat should be really tender.
Meanwhile make the dumplings. Sift the flour and baking powder into a large bowl; add the margarine, cut into cubes and rub into the flour until the mixture resembles breadcrumbs.
add the water and quickly mix well to form a soft dough. Turn the dough onto a floured work surface and cut into eight pieces. Lightly shape to form balls.
Remove the casserole from the oven, add the potatoes then top with the dumplings and return to the oven for a further 25-30 minutes, turning the dumplings over halfway through if you like.