Cooking vegetables with butter and water
The word you are looking for is glazing.  

Quote from source:


  Glazing, a technique taught in culinary schools but underutilized in home kitchens, quickly renders root vegetables (like the yellow beets and carrots pictured) sweet, tender, and glossy. Start by cutting vegetables into uniform pieces and arrange them in a single layer in a sauté pan. Add a few tablespoons of butter, a dash each of salt and pepper, and a pinch of sugar. Add water to nearly cover the vegetables; lay a piece of parchment paper on top; and simmer. As the water cooks off, fat from the butter combines with the vegetables' starches and sugars to form a rich glaze; a shake of the pan distributes it throughout, transforming humble vegetables into elegant side dishes.