Peel the rhubarb stalks, remove woody parts, quarter lengthwise and cut stalks about 5 cm long. Peel and finely chop the shallots. Sauté in butter (1) until light yellow. Stir through veal stock and mustard powder, then add port. Add to the shallots form and cook until half done. Place the rhubarb stalks in the stock and cook on a low heat with the lid on for four to five minutes. Lift out and drain. Set the stock aside.
Rinse fresh spinach, place in a frying pan dripping wet and steam until tender and collapsed. Drain and squeeze well. Start or defrost frozen spinach if necessary.
Carefully pound veal patties between plastic wrap until thin. Season with salt and pepper. Then cover with a little spinach and three or four rhubarb stalks, roll up and tie with kitchen string or fix with wooden skewers.
Fry the veal rolls in the hot clarified butter on all sides. Pour in the reduced stock and steam the rolls on a low fire for about ten minutes with the lid closed. Remove from the sauce and keep warm.
Add the butter flakes by flakes to the slightly boiling sauce form and incorporate. Season strongly with salt and freshly ground pepper and pour over the rolls.
Tip: Did you know that one bowl of spinach already covers the entire daily requirement of vitamin K and beta-carotene?