Step 1Bring a pot of salted water to a rolling boil and blanch the carrots for 1 to 2 minutes, until just tender. Drain and set aside.
Step 2Melt the butter in a large saute pan over medium heat. Add the leeks or scallions and cook 2 to 3 minutes, then add the carrots, favas, peas and asparagus tips. Season with salt and pepper and cook, stirring, 2 to 3 minutes.
Step 3Add the demi-glace or stock. Lower the heat, cover the pan and simmer until the vegetables are just tender, about 5 to 10 minutes. Stir in the chervil and serve.