1. To make Filling: Heat oil in skillet over medium-high heat. Add onions, and sauté 7 minutes, or until beginning to brown. Add thyme and garlic, and sauté 1 minute. Remove from heat, and stir in artichokes, olives (if using), parsley, and zest. Cool.

2. To make Dough: Place flour, butter, sugar, and salt in bowl of food processor; pulse until mixture resembles fine meal. Add eggs and milk, and pulse until Dough comes together. Shape into log. Slice log into 12 rounds. Roll out each round into 1/8-inch-thick circle with rolling pin on well-floured work surface.

3. Preheat oven to 375°F; coat baking sheet with cooking spray. Brush Dough rounds with beaten egg (if using). Spoon 2 heaping tsp. cheese in center of each Dough round, then top with 3 Tbs. Filling, leaving 1-inch border. Sprinkle each tart with 2 tsp. cheese, then fold in edges to partially cover Filling. Brush edges with beaten egg (if using), and sprinkle with salt, if desired. Bake 20 to 30 minutes, or until tarts are golden.