Peel, then trim ends of carrots and parsnips. Cut the vegetables in half lengthwise.
In a 5- to 6-quart pan over medium-high heat, melt butter. Add carrot halves and 3/4 cup water; cover and cook 3 minutes.
Add parsnip halves, cover, and continue cooking until vegetables are tender when pierced, 8 to 10 minutes longer.
Uncover the pan and shake it frequently until liquid has evaporated. Pour the vegetables into a bowl and add salt to taste.