8 ounces (1 1/4 cups) rhubarb, cut into 1/2-inch pieces
1/4 cup sugar
2 tablespoons firmly packed brown sugar
1 tablespoon corn starch
1/8 teaspoon salt
1/2 teaspoon freshly grated lemon zest
1/2 teaspoon vanilla
1 1/2 cups all-purpose flour
1/4 teaspoon salt
2 to 3 tablespoons ice water
1 tablespoon water
White decorator sanding sugar
Lollipop or craft sticks
Combine rhubarb, sugar, brown sugar, corn starch and 1/8 teaspoon salt in saucepan. Cook over medium-low heat 10 minutes or until bubbly and thickened. Remove from heat; stir in lemon zest and vanilla. Cover; refrigerate until completely chilled.
Combine flour and 1/4 teaspoon salt in food processor bowl fitted with metal blade. Add butter; pulse until mixture resembles coarse crumbs. Add 1 tablespoon water at a time, pulsing between each addition, just until dough forms. Shape dough into disk; flatten slightly. Wrap in plastic food wrap; refrigerate 1 hour or until firm.
Heat oven to 375ºF. Line baking sheet with parchment paper; set aside.
Place egg and 1 tablespoon water in bowl; beat with whisk. Set aside.
Roll out dough on lightly floured surface to 1/8-inch thickness. Cut dough into circles, using 4 1/2-inch round biscuit or cookie cutter. Cut each circle in half; brush edges with egg wash. Place rounded teaspoon filling onto one side of dough. Place craft stick along edge of filled half. Fold remaining dough over filling; crimp edges using fork. Cut small "x" in top of dough to vent. Brush top with egg wash; sprinkle with sanding sugar.
Place onto prepared baking sheets; bake 13-15 minutes or until edges are golden brown. Cool on baking sheet 10 minutes; transfer to cooling rack. Cool completely.
TIP: Filling may need to be mashed or coarsely chopped before using, depending on the size of rhubarb pieces used.
VARIATION: Substitute fresh blueberries or chopped strawberries for the rhubarb in the filling.