Place the whole potatoes in a large pot, cover with water, and bring to a boil. Lower the heat and simmer until half-cooked and almost tender, about 15 minutes. Drain and let sit until cool enough to handle. Slip the skins from the potatoes and cut into 1/2-inch dice.
Heat the oil and melt the butter in a medium skillet over high heat. Add the onions and cook, stirring, for 2 minutes. Add the garlic, and cook, stirring, for 20 seconds. Add the potatoes, essence, thyme, salt and pepper, and cook without stirring, but shaking the pan occasionally to keep from burning, until the potatoes begin to color and crisp on the underside, about 4 minutes. Turn the potatoes with a spatula being careful not to mash, and continue cooking until uniformly golden.
Remove from the pan and serve hot.
Makes 2 to 4 servings.