Place the meat in a deep tin and coat with plain flour. Finely cop the onion and celery, peel and dice the carrots, quarter the mushrooms and add all to the meat.
Add the fresh thyme, garlic, balsamic vinegar and tomato base sauce. Add a little water to thin the sauce, cover with a lid and cook in the preheated oven for 2-2.5 hours. The meat should be really tender.
To make the dumplings (if using) - Sift the flour and baking powder into a large bowl, add the cubed margarine and rub tint 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. Cook either on the stew or in a pan of simmering water for 20 minutes - the dumplings should be light and fluffy in texture.
Adjust the seasoning as required and serve immediately.