Shaanxi-Style Chili Oil

1. Heat the oil in a frying pan over medium-high heat until the oil just starts to smoke or waves start forming on the surface. Test by adding a pinch of crushed chili pepper into the oil; it should sizzle. Be careful not to overheat the oil.
2. Remove the saucepan from heat. Add crushed chili pepper into the hot oil and give it a quick stir.
3. Add sesame seeds and salt. Let the chili oil cool down for 30 seconds. Carefully add vinegar to the hot chili oil.
4. Let the chili oil cool down to room temperature. Transfer the chili oil into an airtight glass container. Seal and refrigerate.