Mix together the flour, salt, and sugar in a stand mixer fit with the pasty hook, or mix by hand. Mix in the butter or cut it in with a pastry cutter. Slowly add in the water until the dough is flaky but comes together when squished with your hands. If it won’t come together, add in water 1 tablespoon at a time until it does.
Roll the dough into a ball and divide in two. Roll each ball out into a 1-inch thick disc. Wrap and place in the refrigerator to chill for 1 hour.
Pit and wash cherries. In a mixing bowl, mix the cherries with the sugar, fresh lemon juice, cornstarch, and cinnamon. Set aside.
After 1 hour, remove the dough from fridge. Preheat oven to 375F and grease a muffin tin. On a floured surface, roll out each disc of dough to a 1/4 inch thick. Using a wide-mouth Mason jar band, cut out 12 rounds from each disc. Roll each round out to about 5-6 inches in diameter. Fit 12 rounds into the greased muffin tin.
Fill each pie crust with a heaping amount cherry pie filling, but make sure it’s not overflowing to the edges of the crust.
Using the other 12 rolled out rounds of pie crust, either place them over the pie filling and cut slits in the top or cut the rounds into 1 cm strips and use the strips to create a lattice on top of the pie. Before placing your top crust on, mix together egg yolk and water and brush the egg wash along the edges of the bottom pie crust—this sticks the bottom and top pie crust together.
Press edges together with a fork and trim excess crust around the edges with a small knife. Brush the tops with the egg wash and sprinkle cinnamon sugar over the crusts (1 tablespoon sugar and 1 teaspoon cinnamon.) Bake for 30-35 minutes or until the tops are golden brown.