Heat butter – or oil – in a saucepan, add onions and sauté until translucent. Stir in meat and roast until golden brown. Sprinkle with cinnamon, pour in water, season heavily with salt and freshly ground pepper. Bring to a boil, cover and simmer at low temperature until cooked through (approx.
1 1/2 hours).
Soften rhubarb pieces in butter for a few min, add juice of one lemon, stir and continue cooking for 2 to 3 min. Add to meat, simmer gently for 10 min.
Serve hot with long grain rice.