Step 1

Cut each rib strip between the bones or cartilage into individual riblets. In a large bowl, combine the onion, sugar, pepper, and 3 tablespoons of the fish sauce and mix well. Add the riblets and use your fingers or a large spoon to mix well, coating all the riblets evenly. Cover with plastic wrap and refrigerate for at least 2 hours or up to overnight.

Step 2

Remove the bowl from the refrigerator about 45 minutes before searing. For the best flavor, use a grill to sear the riblets. Prepare a hot charcoal fire (you can hold your hand over the rack for only 2 to 3 seconds) or heat a gas grill to high. Remove the riblets from the marinade, reserving the marinade, and sear the riblets on the grill on all sides, turning as needed, for about 10 minutes total. Some charred edges and grill marks will deepen the flavor.

Step 3

Alternatively, position a rack as close to the heat source as possible and preheat the broiler for 20 minutes to get it nice and hot. Line a baking sheet with aluminum foil and arrange the riblets on the pan. Broil, turning once, for 6 to 8 minutes on each side, or until tinged brown and a bit charred.

Step 4

Transfer the seared riblets, the reserved marinade, and any cooking juices to 6-quart Instant, and add the remaining 3 tablespoons fish sauce, the caramel sauce, and water almost to cover (about 2 cups). Lock the lid in place then program to cook at high pressure for 13 to 15 minutes (use more time if you want tender ribs; I use less time because I like a bit of chew). Once done, let the Instant Pot depressurize naturally for 12 minutes before releasing pressure and unlocking the lid. (Or, cook the ribs in a 5-quart Dutch oven. Simmer them, covered, for about 45 minutes; resist removing the scum that rises to the top because it’s part of the flavor.)

Step 5

Regardless of cooking vessel, bring the ribs to a vigorous simmer (use saute on the Instant Pot), and cook for about 20 minutes, or until the riblets are tender when pierced with the tip of a sharp knife. You should be able to bite through a piece of cartilage easily but a slight crunch should remain. The sauce will have reduced somewhat, but there will still be a generous amount.

Step 6

Remove from the heat and let stand for a few minutes so that the fat collects on the surface, then use a ladle or spoon to skim it off. (Or, let cool, cover, and refrigerate overnight to congeal the fat, making the task much easier; reheat before continuing.) Return to a simmer and taste the sauce. Add extra fish sauce to create a deeper savory flavor, or water to lighten the flavor.

Step 7

Transfer the riblets and sauce to a shallow bowl and sprinkle the green onion on top. Serve immediately.