Season the steaks with the spices salt, pepper, garlic, and onion powder on both sides. You can choose to let it marinate for 15 minutes or cook right away.
Select the "Sauté" mode on the electric pressure cooker. Let it heat up, and add the oil to heat it.
Brown the slices on both sides for about 1 minute on each side. Remove from the pot and reserve.
Without rinsing the pot, add the onion and sauté for 5 minutes, trying to remove whatever is stuck to the bottom of the pot.
Press the "Cancel" button. Add a cup of water, the peppercorns, and the eye of round slices. Make sure to remove any bits stuck to the bottom to avoid having the instant pot “BURN” error.
Cover the pot and move the valve to where it says “Sealing” to start building pressure. Press the option "Pressure Cook" or “Manual” and select the time. Depending on how thick your slices are, you can adjust between 9 to 12 minutes if it is very thick. For these, set to 10 minutes. It takes 10-12 minutes to reach pressure.
Once the time is up, let it sit for 10 minutes and then move the valve to “Venting” to remove any additional pressure it may have.
Remove the eye of round steaks from the pot and place them on a plate. Remove ½ cup of the liquid from the pot and dissolve the cornstarch with it into the small bowl. Select the "Sauté" option, add the dissolved cornstarch, stirring to ensure that it mixes well with the rest of the liquid and that it does not get all in one place.
Add the butter and cook until the sauce thickens or for about 3-5 minutes. Add the tenderloin slices again and cover with the sauce.
Press the "Cancel" button and serve the round steaks. Enjoy!