Whisk piloncillo, soy sauce, sesame oil, chile, garlic, ginger and ¼ cup water in a heavy medium saucepan over low heat until piloncillo dissolves. Transfer to bowl and cool completely. Add ribs and toss to coat. Cover bowl with plastic wrap and cover and refrigerate at least one hour or overnight.

Heat oven to 450 F. Remove ribs from marinade and place curved-side up on a rack set over a rimmed foil-lined baking sheet. Roast for 20 minutes.

Meanwhile, stir the marinade in a heavy medium saucepan over medium-high heat 20 minutes or until thick and syrupy.

Flip the ribs and cook, basting frequently with reduced marinade, until ribs are tender, about 20 more minutes. Transfer ribs to platter and sprinkle with green onions.