Begin by making lime pastry dough. Whisk flour, half of the sugar, salt and half the lime zest in a large bowl. Cut cold butter into cubes and work into flour mixture until only pea sized pieces remain. Add egg yolks and ice water, stirring just until the dough begins to come together. If dough is too dry add more ice water. Be careful not to over mix. When it starts to form a ball, divide dough in half and wrap each piece with plastic wrap then flatten into a disc. Refrigerate at least 1 hour.
2 ½ cups all purpose flour, ½ cup granulated sugar, 1 cup unsalted butter, ¼ teaspoon salt, ⅓ cup ice water, 2 teaspoons lime zest, 2 large egg yolks
Meanwhile make homemade pie filling. In a small saucepan over medium heat stir frozen cherries, remaining zest, lime juice, remaining granulated sugar, cornstarch and a pinch of salt to a boil. Then reduce heat to medium low and simmer until most of the liquid is evaporated about 15 minutes, smashing cherries with a spoon and stirring frequently, until mixture is thickened. Then remove from heat and allow filling to cool.
On lightly floured surface roll pastry to ⅛" thick. Using a large cookie cutter cut as many shapes as possible, re-rolling scraps and continuing to cut until dough is gone. Refrigerate or freeze pastry shapes until cherry filling is cool.
When ready to bake preheat oven to 375 degrees Fahrenheit and prepare baking sheets with parchment paper or silicone liners.
Place 1 tablespoon filling into the center of half of the dough shapes. And cut small vent holes in the other half. Run water along edges of the filled dough with finger then top with the unfilled pieces. Press edges to seal with a fork, being careful not to stretch edges too thin.
Beat egg whites and brush evenly over heart shaped pastries then sprinkle with coarse sugar.
2 large egg whites, ¼ cup coarse sugar
Bake 20-25 minutes until golden brown.
Transfer to wire rack to cool. Enjoy warm or at room temperature.