Here are some basic steps to perfect mini-pies:
A recipe for one standard pie filling (around 4 cups) and two to three single pie crusts should be enough to make a dozen or so pies.
For fruit or nut fillings, chop the ingredients smaller than you would for a normal pie, so they fit and are proportional.
Use a small round cake pan or bowl to cut the dough for the crusts — you'll want circles about 5½ inches in diameter to form each mini pie.
Don't overfill the pies or the filling will spill over as they bake. For single crust and lattice-top pies, fill to just below the muffin tin line, about one-fourth inch below the top of the crust. For double-crust pies place the vent holes toward the top of the pies to reduce spillage as they bake.
Use non-stick muffin tins (two sets of 12-cup tins will work for a dozen pies), and grease the cups before filling to make sure the little pies don't stick when they're done. Bake one tin at a time, in the center of the oven. The darker the finish on the pan, the faster the crust will bake.
Unlike a standard pie, in which the crust bakes more quickly than the filling, the opposite is true with a mini-pie: the filling bakes faster. Keep this in mind when baking delicate custard pies, like pumpkin; for these pies, you may need to par-bake the crust before filling, or cook the filling completely before adding to the finished crust.
Don't fill every cup in the muffin pan. Alternate, filling every other cup to allow enough room to form and finish the outer crust. Filling every other cup helps the heat circulate better when baking the crust. And it also gives you extra room to wiggle the pies out when they're done.
When the pies are done, give them a gentle twist in the pan to loosen so they don't stick, rotating each pie in the cup every few minutes or so. When the pies are somewhat cooled and set, remove the pies to a rack.
Invest in some tiny cookie cutters, if desired, to help decorate and garnish the pies. The cutters are available at cooking and baking supply stores, as well as online.