• Prepare your pie dough if making from scratch, and allow to chill at least one hour up to overnight in the fridge. You can use use your favorite homemade or store-bought dough, but I recommend one with a lot of butter. This recipe is my favorite!

Make the Filling

• Combine the fruit, granulated sugar, lime juice, lime zest, and salt in a large measuring cup or bowl. Let it sit until the sugar has dissolved and the mixture is syrupy.
• Scrape the filling into a large non-stick skillet, and bring to boil over medium high heat. Add the cornstarch, reduce the heat, and allow the mixture to simmer for 15-20 minutes, stirring often. The plums will begin to break down slightly and the syrup will thicken. Do not let it get too thick – it should be the constancy of loose honey. Stir in the rum, let it simmer for another 2 minutes, and remove from heat.
• Let the filling cool before making your pies. Once room temperature, I recommend chilling the filling in the fridge for at least half an hour for best results.

Assemble the Pies and Bake

• Once the filling is nearly cooled, heat the oven to 375°F and prepare your muffin tins. Spritz the inside of the muffin cups with non-stick cooking spray and set aside, away from the preheating oven so that they stay room temperature. 
• Keeping unused portions in the fridge to keep cold, roll out your dough on a well-floured surface in batches to a thickness of 1/8-1/4 inch. Using a cookie cutter or stencil, cut out 6 inch circles from the dough and press them gently into each muffin cup – You should use about two-thirds of the dough for the bottom crusts. The circles don’t have to be perfect, but you should try to have at least a quarter inch of dough overlapping the top of the cups. If your pie filling is not yet chilled enough, place the prepared pie crusts in the fridge. Once the filling is cooled, you can fill each crust nearly to the top with about 2 spoonfuls of filling and place the muffin tin back into the fridge to chill as you prepare the pastry lids.
• Roll out the remaining third of the pie dough the same thickness at the bottom crusts, and set them out on a tray or baking sheet. Cut hashmarks or a tiny circle out of the center of each top to allow for steam to vent while cooking. 
• Remove the chilled half-constructed pies from the fridge. Working one at a time, place each pie top over the filling of each pie. Crimp the edges of the pie, sealing them tightly. Once all the pies are constructed, brush the tops with egg wash and sprinkle with a pinch of raw sugar. Chill in the freezer for a short 10 minutes, and then bake in the pre-heated oven for 30-40 minutes, until the tops are golden. Remove from the oven, and let them sit for 10 minutes before gently removing them from the muffin tin. Serve warm immediately -preferably with a scoop of ice cream! - or allow to cool completely, and follow the directions for storing, below.