Turn the Instant Pot to saute and let heat until it reads HOT, or for 2-3 minutes.
Add in 1 teaspoon of the oil. Pierce each brat several times with a fork and then place the brats into the oil and sear on each side until browned, about 2 minutes per side. Once browned, remove the brats and place them onto a clean plate.
Add the remaining teaspoon of oil and onion and saute the onion for 2-3 minutes, or until just beginning to soften.
Turn the pressure cooker off and add in the beer, or stock, and use a wooden spoon to scrape up any browned bits on the bottom of the inner pot.
Add the brats back to the inner pot and spoon the sauerkraut over the brats.
Set to cook on high pressure for 6 minutes. Once the cook time has elapsed, allow the pressure to release naturally on its own for at least 10 minutes.
Serve the bratwurst with the onions and sauerkraut on buns with mustard or plain as desired.
Storage: Leftover Instant Pot Brats can be stored in an airtight container for up to 3 days in the refrigerator. Reheat in the microwave-safe dish in 1-minute intervals until warmed through.Beer: Use any beer you like, keeping in mind that a pale lager will not overwhelm the flavor of the brats. You can also, omit the beer and use chicken stock in its place. You can skip sauteeing the brats. Just keep in mind that the exterior of the brats will be soft, much like a boiled brat. You can finish on the grill or under the broiler to crisp up if desired.Preparing with Peppers and Onions: If you like your brats served with peppers and onions instead of sauerkraut, saute 1 large sliced onion and 2 large sliced bell peppers (any color), after browning the bratwurst. Deglaze the pan with beer or stock and add the brats back to the pressure cooker. Omit the sauerkraut and cook as the recipe directs.Increasing the recipe: You can cook up to 8 bratwursts in the Instant Pot without having to change the amount of beer or sauerkraut or the cooking time. However, you may need to brown your bratwursts in batches. If you want to prepare more than 8 brats at a time, I would suggest doubling the beer, onions, and sauerkraut. Keep the cooking time the same. Sauerkraut: Feel free to omit from the recipe if you don't care for sauerkraut.