I'm going to copy what Isa writes on her site- her directions are much better than what I can write. Go ahead and give these a try!
If some of the filling is sneaking its way out, then use a little less filling with the next one. Once you get the amount of dough down, you can do a few at a time in assembly line style. I usually do six, lay out the circles, add the filling, pinch them closed. This works out perfectly if you time it with the boiling.