Place boniatos in a medium saute pan and cover with milk. Cook boniato in milk until tender.
Meanwhile, heat oil in a small saucepan until almost smoking, add garlic, shaking pan constantly and season with salt and pepper. When the garlic turns golden brown, add the lime juice. Set the mojo aside until the boniato is done.
Drain boniato, and while still hot, puree the boniato through a food mill or mash with a potato masher; add the mojo and season with salt and pepper.