Fresh, soft Greek whey cheese forms the filling for this tart by Diane Kochilas, flavored with mastic, a Greek spice. If you can find it, use either myzithra made from sheep's or cow's milk, or anthotyro, made with sheep's or goat's milk. Otherwise, use the freshest ricotta you can find.
Combine the flour, baking powder, sugar, and salt in the bowl of a food processor outfitted with a dough blade. Cut the butter into small pieces and mix with the shortening in a separate bowl. Add the butter mixture to the flour mixture and pulse on and off until smooth. To the flour mixture, add the eggs, orange-blossom water, and milk. Pulse on and off to form a smooth dough.
Remove the dough, cover in plastic, and let rest for 1 hour.
In a medium-sized bowl, combine the cheese, sugar, whole egg, mastic, and 1 cup of the flour. Mix so that all ingredients are thoroughly blended. (The mixture shouldn't be pasty, but it shouldn't be watery either. If the mixture is very loose, add more flour.)
In a large bowl and with an electric mixer set on high speed, beat the egg whites until stiff but not dry and quickly but gently fold cheese mixture into egg whites.
Preheat the oven to 350 degrees. Lightly butter a large baking sheet.
Break off a small piece of dough (a bit larger than an unshelled walnut) and roll it into a 4-inch circle. The dough should be at least as thick as a quarter. Place a rounded teaspoon of cheese filling in the center of the dough and pinch the edges of the dough together to make an ersatz tartlet. Repeat with remaining dough and filling.
Place the melitinia on the baking sheet and bake until the cheese mixture has solidified and dough is a light golden brown, for 20-25 minutes. Remove the baking sheet from the oven and place on a wire rack to cool. Sprinkle the melitinia with cinnamon before serving. Store covered in the refrigerator.