Finely dice the onion. Peel the carrots and cook them in vegetable stock until they are cooked through but still slightly firm to the bite. Drain, catching some of the vegetable stock. Pour about 2 - 3 tablespoons of the hot broth over the onions and let them steep. Then add vinegar, oil and mustard and season well with salt, pepper and a little garlic (granules or fresh).
Cut the carrots into slices and add to the dressing, mix well and let steep for 1 hour. Season again to taste before serving, as the carrots take a lot of seasoning. If necessary, add a little vegetable stock. If you like, you can sprinkle with fresh parsley.
Instead of vegetable stock cubes I use homemade vegetable paste, because it is nicely spicy and tastes better.