Saute aromatics: Set the instant pot on SAUTE & set it on HIGH heat. Add oil and when the oil becomes moderately hot gently release the onion and garlic and saute until the onion begins to turn limp. Add salt to quicken the process of sautéing.
Rinse Rice: While the onion and garlic are being sautéed rinse the long grain white rice several times under running tap water (Cold or normal temp.) until absolutely clear water runs through. This is super important & will help rinse out the surface starch from the rice. As a result you'll have fluffy Mexican rice, no more gummy/mushy rice & NO burn error! Drain the rinsed rice in a colander to remove excess water. DO NOT soak the rice in water, this will alter the cook time!
Toast rinsed rice: Add the rinsed & drained rice back to the pot & toast the rice for 1-2 mins stirring continuously with a spatula. You'll notice the rice will begin to turn opaque, some grains might pop, that's absolutely fine. Toasting the rice will enhance the depth of flavor & take the dish to the top. TURN OFF the instant pot.
De-glaze pot: Now pour the chicken stock into the pot and de-glaze the pot very well by scrapping the sides and the bottom of the pot to loosen any stuck food particles. This will prevent the BURN! Add the chili powder, the cayenne pepper (both optional) and the tomato sauce and give everything a quick stir. READ NOTES BELOW #7 (It's important).
Pressure cook: Now, secure the lid of the instant pot, seal the valve and PRESSURE COOK on HIGH for 6 mins for al dente rice or 8 mins for softer rice. Once, the cooking cycle is over the instant pot will begin to beep. Allow the pressure to release naturally for 10 mins and than release the rest of the pressure manually by turning the valve from the sealing to the venting position. Open the lid carefully and TURN OFF the instant pot immediately.
Fluff Rice & serve: With the help of a pair of fork fluff the rice gently and immediate remove the steel insert of the instant pot and keep it on the counter top to prevent the rice from getting over cooked by the residual heat & getting stuck at the bottom of the pot. Or you may transfer the fluffed Mexican rice into a serving bowl. Serve hot with your favorite Mexican dishes and enjoy!