n a large bowl, mix all the ingredients for the tefteli. Roll the mixture into golf-ball-size meatballs.
Add the oil to a deep, heavy-bottomed pan and heat over medium-high heat. You should use enough oil to cover the bottom of the pan entirely. Once the oil is hot and shimmering, add the tefteli and sear them on all sides until golden brown. To ensure even browning, don't overcrowd the pan and fry the tefteli in batches. Once all tefteli are done, transfer them to a platter.
To the same pan, add one tablespoon of oil and the chopped onion. Saute the onion over medium heat for 5 to 7 minutes, until translucent, scraping all the delicious meat pieces that stuck to the bottom of the pan.
Then, add the tomatoes and bring everything to a gentle simmering. Pour in the heavy cream and add the basil leaves. Season the sauce with salt, sugar, and pepper.
Add the tefteli to the pan, cover with the lid, and let them slowly simmer for 20 minutes. Adjust the seasoning to taste and remove from the heat.