Pick over the purslane, discarding thick heavy stems. Pile into a strainer and rinse thoroughly. In a heavy deep skillet, heat the oil and saute the onion, just until glazed. Add the garlic. Pile the verdolagas in the pan. If the pan doesn't sizzle, add 1 or 2 tablespoons water. Cover and steam for 2 minutes. Open the pan, stir and add salt, pepper, and cubes of cheese. Close the lid for another minute or two. Serve along with the potlikker.