Start by making your crust. Combine the flour, sugar, salt and cinnamon in a large bowl. Add the butter and cut it in using a pastry cutter, or a fork and knife (which is what I usually do). You can use your hands a bit at the end to break the butter up, but do it quickly since it’s best to keep the butter as cold as possible – you don’t want it to melt! Keeping small chunks of cold butter in the dough is essential if you want a flakey crust – when you bake it, the butter balls melt and create those amazing buttery, flakey pockets that make homemade pastries so delicious.
Mix half the egg (save the other half for later), the ice water, and the apple cider vinegar together, then add to the flour mixture and stir until just combined.
Form the mixture into a ball and wrap tightly in plastic wrap, and then chill in the fridge for an hour.
While your dough is chilling, prepare the filling. Sauté the onions in 1 tablespoon of olive oil over medium heat for one minute. Add the sugar to the onions and continue to sauté on low heat for an additional 30 minutes until they become very soft and caramelized.
Once the onions are done cooking, combine them with the chopped pears, cheddar, rosemary and salt and pepper in a large bowl. Set aside.
Roll out the dough onto a floured surface and cut into circles (you can make these as big or as small as you like. I made mine about 6-8 inches in diameter so they’d be easy to fit in your hand, but you could also make them bite-sized for a more elegant appetizer, or if you’re feeding a larger group.
Spoon a small amount of the pear filling onto each of the cut pastry circles, then fold in half to create a half-moon shape.
Press the edge of a fork around the side of each pastry to seal them and to add a bit of a decorative edge. Use a knife to create a small slit in the top of each pastry to act as a vent.
Use the remaining half of the egg to brush atop each pastry. Sprinkle with sea salt, if desired.
Bake the pastries on a parchment-lined pan for 35-40 minutes at 375 degrees. Remove from the oven and allow to cool slightly before serving.