Trim beef heart of the thick outer layer of fat. There’s no need to try to get every bit but I take off the big, tough chunks. Also, look for the veins and arteries and remove them. They get tough and stringy, which is not what you want in your stew. Dice the heart into bite sized pieces.
Melt 1 tbsp of the lard in a large skillet on medium heat. Place the oxtail pieces in the skillet and brown on all sides, about 3 minutes per side. Place each piece in your Instant Pot pan or a soup pot once they are browned. If you’re short on time, skip this step and just put the oxtail in the pot. It will still taste great!
Put the diced beef heart into the pot on top of the oxtail.
Melt the remaining tbsp of lard in your skillet and saute the onion over low heat until soft. (You can skip this step, too, if you’re short on time!) Add the garlic for one minute. Add the onion mixture to the pot.
Deglaze your skillet by putting the wine in the skillet and turning heat to high. Reduce the wine by half, scraping up any bits of meat that may be left from browning. Add it all to the pot. If you don't want to use wine, you can deglaze the pan with broth.
Dice carrot and parsnip into bite sized pieces and add to the pot, along with the thyme, rosemary, salt, pepper and beef broth.
If using an Instant Pot, place the pot in the device and close the lid. Make sure that the vent is turned to “Sealing”. Set the pressure to high and the time to 75 minutes. Once the time is up, let it come down from pressure on its own.
Once the pressure is released and the red button on the lid pops up, remove the lid. I like to take the oxtail pieces out and move any remaining meat from the bones so I can put the meat back into the soup. Save the bones for your next batch of beef broth!