Peel the boniato and cut it into 2-inch chunks, dropping each piece into a bowl of cold water as you go so it does not discolor.

Drain the chunks and put them in a large pot. Cover with cold water by 1 inch and add 1 tablespoon kosher salt.

Bring to a boil, then reduce to a steady simmer and cook 18 to 25 minutes. Start testing at 15 minutes: a paring knife should slide in with almost no resistance.

Drain well and pile the chunks into a warm serving dish.

While the boniato cooks, warm the olive oil in a small skillet over medium-low heat.

Add the sliced garlic, onion and cumin. Cook 4 to 6 minutes, stirring, until the onion is limp and the garlic is pale gold at the edges. Do not let the garlic brown.

Take the skillet completely off the heat and wait about 30 seconds.

Pour in the sour orange juice, then stir in ¾ teaspoon salt and the black pepper. Taste and adjust the salt.

Pour the hot mojo over the drained boniato, garlic slices and onion included.

Let it rest 5 minutes so the starch absorbs the sauce.

Scatter the chopped cilantro over the top if using, and serve warm or at room temperature.