Trim off excess fat. Rinse the oxtail pieces and let them sit in cold water for 10 to 20 minutes to draw out excess blood. Drain well, and pat dry with paper towels.
Press the “Saute” button on the Instant Pot. When the pot is hot, add 1 tablespoon of canola or vegetable oil. Sear the oxtail pieces in two batches, browning all sides. Or sear in separate pan and place in Instant Pot
Combine ingredients for braising liquid and pour the braising liquid over oxtails. Add the vegetables.
Close the lid tightly. Press the “Meat” function, and using the “+” button, increase the time to 45-48 minutes. 48 minutes for softer meat. When finished, the Instant Pot will automatically turn to the “Keep Warm” mode. Leave the pressure cooker alone for about 10 minutes before opening the lid.
Stir in the scallion and the sesame oil. Remove the meat and vegetables from the pressure cooker. Strain the cooking liquid into a bowl to skim off the fat. Pour sauce over the ribs.
Garnish with the optional scallions and sesame seeds. Serve with hot rice.