Place lean ground beef and onion in a large, deep skillet over medium-high heat. Cook until beef is evenly brown and onion is soft. Drain and turn heat to medium-low.

Pour in condensed cream of mushroom soup. Mix in processed cheese and desired amount of jalapeño peppers. Cook and stir until well blended, about 10 minutes.

Transfer the mixture to a medium bowl. Cover and chill in the refrigerator 8 hours, or overnight.

Reheat the mixture in a slow cooker, mixing in about 1 tablespoon of water to thin if necessary, before serving.