Heat butter in a large, deep saute pan over medium-high heat. Carefully add pearl onions; saute until golden brown, about 5 minutes. Remove pan from heat. (Can be prepared to this point a couple of hours ahead.)

Add asparagus, carrots, snow peas, artichokes, salt and 1/2 cup water to pan. Return to high heat; cover and cook until vegetables start to steam. Steam, covered, until almost tender, about 5 minutes. Add peas; continue to steam until vegetables are just tender, about 1 minute longer. Stir in scallion tops, and season with pepper and more salt, if necessary. Serve immediately.