• To make the crust, sift the flour onto some baking paper and then add it to a food processor.
• Add the sugar, and salt and pulse a couple times to mix.
• Add about half of the butter and pulse several times.
• Then add the rest of the butter and pulse 6 to 8 times until the largest pieces of butter are about the size of large peas.
• Sprinkle the mixture with about 2 tablespoons of the ice water (leaving the cubes behind) then pulse again.
• Then add more ice water, a tablespoon at a time, pulsing once or twice after each addition until the dough just barely begins to hold together.
• You know that the mixture is ready if when you pinch some together with your fingers and it holds together. Be careful with the amount of water you add, too much and the crust will be tough.
• Empty the crumbly dough mixture from the food processor onto a clean, dry, floured surface.
• Form a mound with the mixture and knead briefly (just a couple of turns). Form into a ball, cover with plastic wrap and chill for at least 1 hour (although it can be up to a few days or even frozen at this point).
• Once chilled, let the dough sit at room temperature for 10 minutes before rolling.
• Roll out the crust on a lightly floured surface to about ¼ inch thick.  Using 4½ cutter, cut out twelve circles and line 12 sections of a muffin pan with the circles. The dough should overlap enough to be able to crimp the edges.
• Prick the bottom of each one with a fork and chill in the pan in the fridge while you make the filling.
• preheat the oven to 350F/175C

For the filling:

• Heat the oil in a lidded frying pan, add the red onions and cook over high heat for 2-3 minutes, stirring often to keep them from sticking to the pan.
• Lower the heat, cover and cook for 8-10 minutes until soft.
• Add the vinegar. sugar, and honey and cook for 10 minutes, stirring occasionally until the onions are caramelized.  Season to taste with salt & pepper if desired and set aside to cool.
• Put the feta cheese, cream cheese, egg, and half the parsley in a food processor and blitz until smooth.
• Fill the chilled tart crusts with 1 tablespoon of the onion mixture and flatten with the bottom of the spoon.
• Pour cheese mixture over the onions.
• Bake for 20 minutes, or until the pastry is crisp and the filling is just golden brown and set Sprinkle chopped parsley and serve. These tarts are good warm or cold.