Various things. The basic recipe is cream cheese or a mix of cheeses. Some add tomato, or sun dried tomato.
lol, I made a lot for a couple of friends a few years ago. But I worried that they wouldn't be hot enough, because it was early in the season, and so I added some chopped hotter peppas to the mix. The heat was BLAZING....
So taste a bit of your jalapenos first. The kind you buy at the supermarket can be very mild, but the ones you grow at home aren't.