How to Make It
Combine first 3 ingredients in a large, heavy saucepan over medium-high heat. Cover and cook, without stirring, 5 minutes or until blueberries begin to release some liquid. Uncover and simmer until sugar dissolves, stirring constantly. Reduce heat, and simmer 25 minutes or until mixture thickens, stirring occasionally. Remove from heat; cool completely. Cover and chill. (Mixture will continue to thicken as it cools.)
Stir together flour and next 5 ingredients in a large bowl; cut in butter with a pastry blender until mixture is crumbly. Combine egg and egg yolk in a separate bowl; beat lightly with a wire whisk. Add egg to crumb mixture, stirring lightly with a fork. Sprinkle water, 1 teaspoon at a time, evenly over surface, stirring with a fork until dough is moist enough to hold together. Pat dough into a round disk; cover and chill 1 hour.
Divide dough into 2 portions (about two-thirds and one-third of the total). Place larger portion on a lightly floured surface. (Chill remainder, covered.) Roll pastry into an 11-inch circle (about 1/8 inch thick). Transfer dough to a 9-inch tart pan with a removable bottom. Carefully fit dough into pan (without stretching it). Remove excess dough by rolling a rolling pin over top of pan. Spoon blueberry mixture into pastry.
Roll remaining pastry into a 9-inch circle (about 1/8 inch thick). Cut circle into 8 (3/4-inch-wide) strips, using a knife or pastry wheel. Lightly brush rim of unbaked tart with water. Place 4 strips diagonally across top of tart. Place remaining 4 strips diagonally in opposite direction across top of tart. Remove excess dough. Press edges of strips against pastry shell edges. Place tart on a baking sheet lined with aluminum foil.
Bake at 350° for 40 to 45 minutes or until golden brown. Cool on a wire rack 15 minutes. Remove rim of pan; cool completely on a wire rack. Cut tart into wedges; serve with whipped cream, if desired.