Crust: Lightly beat yolk and 2 tablespoons ice water in a small bowl until combined.
Pulse flour, sugar, and salt in a food processor to combine. Add butter and process until mixture resembles coarse meal, about 15 seconds. With machine running, add yolk mixture in a slow, steady stream. Pulse until mixture holds together; if dough is still too dry, add additional ice water, 1 tablespoon at a time. Shape dough into a disk and wrap in plastic. Refrigerate until firm, at least 30 minutes and up to overnight.
Preheat oven to 375 degrees with racks in middle and bottom. Coat bottom and sides of a 9-inch springform pan with cooking spray. Let dough stand until pliable. On a lightly floured surface, roll out dough slightly thicker than 1/8 inch. Cut out an 11-inch round. Fit into bottom and up sides of prepared pan. Freeze 15 minutes.
Filling: Stir together rhubarb, strawberries, sugar, cornstarch, salt, and lemon juice in a large bowl. Pour into tart shell. Bake, with a foil-lined rimmed baking sheet on bottom rack to catch juices, until bubbling in center, about 1 hour, 15 minutes. (If browning too quickly, tent with foil during last 15 minutes.) Remove from oven. Release sides of pan immediately. Let tart cool on pan base on a wire rack before cutting into wedges and serving warm or room temperature.