Mix together the carrot, shallot, scallions, and turmeric and add the potatoes, cauliflower, and green beans. To make the dressing, stir the mustard powder into the grainy mustard, making sure there are no lumps. Add the honey and vinegar, mix well, then slowly pour in the oil, stirring as you do so to thicken. Dress the salad and season with salt and pepper to taste.