Take the saucepan and add two tablespoons of sesame oil to it. Heat the oil on a medium-high heat and let it heat for a while. When the oil is heated up a little, add scallion and garlic to the pan. Next add some pepper flakes to it. When all these ingredients are added, lower the heat to the medium and stir it up with a stirrer. Let the process continue for 3 to 5 minutes until garlic starts browning.
Now take a step back and turn on the heat to high. Do not forget to keep on stirring the sauce. Add a small amount of vinegar to the saucepan and let it bring to a boil.
Wait for few minutes after adding the vinegar and then add the dark brown sugar to the pan. Do not forget to stir the mixture and keep on stirring until the sugar is completely resolved.
After the sugar is resolved, lower to heat to medium low and cook it for 10 more minutes. Keep on stirring the sauce often.
Now, let the sauce cool down a little that will even make it a little thicker. The above mentioned ingredients are enough to make 3 large bowls. The sauce can be refrigerated in an air-tight container. Serve and enjoy.