There are four main reasons why you may have some filling leak out. Overfilling - try not to add too much filling, even though I know it's tempting. Not sealed well - this is probably one of the most common culprits... make sure you're brushing the edges with an egg wash, and really pressing to seal. Cracking - if there are cracks in the pie dough, that creates a weak spot, and the filling can seep out there. Not venting - those slits cut in the tops of pies and hand pies aren't just for decoration, they allow the steam that builds up during baking to escape. If you don't have a vent to let the steam out, it can cause the hand pie to sort of burst.