For Crust: Combine flour, sugar, lemon peel and salt in processor. Add butter and proces using on and off turns until mixture resembles coarse meal. Add yol and 2 tabelspoons water adn process again until mixture forms large moist clump. gather dough into ball, flatten into disk and, wrap in plastic wrap and refriderate/chill 30 minutes. (Can be prepared 2 days ahead, let dough soften slightly at room tempoerature before continuing) Divide dough into quarters. Form each quarter into ball, then roll out each quarter into a 6"round. Transfer rounds to four (4") diameter tartlet pans with 1 1/8" sides and removable bottoms. gently press into place. Trim edges and pierce bottom with a fork. Freeze until dough is very firm about 30 minutes.
Pre-heat oven to 400°F. Bake crusts until golden brown, about 15 minutes. Cool crusts completely. (crusts can be prepared up to one day ahead, Cover and store airtight at room temperature.
For Glaze: Bring peach preserves, kirch and lemon juice to boil in a small heavy saucepan. Strain. Cool slightly.
For Filling: Whisk mascarpone cheese, powdered sugar, kirch and vanilla extract in small bowl until smooth. Brush insides of crusts with glaze. Divide filling among the 4 crusts. Arrange nectarine slices attractively atop filling. Brush nectarine slices atop filling. Brush nectarines with glaze. Refrigerate tartlets until filling is set about 30 minutes. (can be prepared up to 4 hours ahead) Remove tartlets from pans and garnish with fresh mint sprigs if desired. Mascarpone is an Italian cream cheese available at gourmet and Italian markets..if unavailable, blend 8 ounces cream cheese with 1'4 cup whipping cream and 2 1/2 tablespoons sour cream. Use 3/4 cup of mixture for recipe
Per serving: 640 Calories; 43g Fat (58% calories from fat); 5g Protein; 65g Carbohydrate; 169mg Cholesterol; 121mg Sodium