Prepare Pastry, below. Wrap and refrigerate (up to 1 hour) while preparing filling.
Preheat oven to 400 degrees F. For filling, in a large skillet cook chard, leeks, garlic, thyme, 1/4 tsp. salt and 1/4 tsp. black pepper in hot oil over medium heat for 4 minutes or until chard wilts and leeks are tender. Cool slightly. Stir in cheese; set aside.
On a lightly floured surface, roll Pastry to a 12-inch circle. Transfer to a parchment-lined greased baking sheet. Spoon filling into center of the pastry circle, leaving a 2-inch border. Fold dough over filling, leaving center open and pleating edges of dough. Bake 30 to 40 minutes or until golden. Serve hot. Sprinkle with parsley. Makes 4 main-dish or 8 appetizer servings
In a large bowl combine flour and salt. Cut up cold butter; cut into flour until mixture resembles coarse meal. Combine water, sour cream, and lemon juice. Add half the sour cream mixture to flour mixture; toss with a fork. Add remaining sour cream mixture; toss with fork until mixture is moistened. Form into a ball.