In a medium pan of boiling water, cook the carrots, uncovered, until crisp-tender, about 3 minutes.
Scoop out with a slotted spoon, and put into a bowl.
Add the potatoes to the same pan of boiling water, and cook until barely tender, about 4 minutes.
Drain the potatoes and add to the bowl with the carrots.
Melt the butter in a large skillet, over medium heat.
Add the carrots, potatoes, cumin, and salt.
Cook, covered, stirring frequently, until the vegetables are tender, 4 to 5 minutes.
Remove the lid, raise the heat to high, and cook the vegetables until they start to brown, about 4 minutes.
Stir in the cilantro.