Shape dough into a disk; wrap in plastic wrap. Refrigerate for at least 1 hour.
In another bowl, combine rhubarb, raspberries, sugar and tapioca; let stand for 15 minutes. Unwrap dough and place on parchment-lined baking sheet. Cover with waxed paper and roll the dough into an 11-inch circle. Discard waxed paper.
Spoon fruit mixture into center of dough to within 2 inches of edges. Fold edges of dough over fruit, leaving center uncovered. Bake at 400° for 25-30 minutes or until crust is golden brown and filling is bubbly. Remove to wire rack. Combine glaze ingredients until smooth. Drizzle over warm tart. Makes 2 servings.
Note: If using frozen rhubarb, measure it while still frozen, then thaw completely. Drain in colander, but do not press liquid out.