Here's a recipe in the video below. The difference is that my mom doesn't use lard, but one egg. Also, she does not roll the dough, instead she pinches off a good size of dough and wraps it around a plum. She never measures the quantities, so she adds less flour and tests to see if the dough holds together when boiling. If it doesn't, only add a bit more flour and knead it until incorporated. If you add too much flour, you can't take it out and the resulted dough will be too hard/ chewy.
The best plums for this, not the ones presented in the video below, are the smaller kind that are found here mostly in central Transylvania. I don't know their exact name. They are much sweater and we usually leave the pip to be removed when eating.
Maybe our Hungarian friends can join in with some tips.