Heat oven to 400°F. Line cookie sheet with parchment paper or silicone baking sheet. On floured work surface, unfold sheet of pastry. With rolling pin, roll to 15×10-inch rectangle. Cut 2 (1-inch) strips from one long edge of pastry, and 1 strip from other long edge. Place remaining pastry rectangle on cookie sheet. In small custard cup, measure 1 1/2 teaspoons of the egg yolk and stir in 1 teaspoon water. Lightly brush rectangle of pastry with egg mixture. To form a rim, place 2 of the long strips on long outside edges or rectangle. Cut remaining strip to fit both short edges of pastry. Brush strips with remaining egg mixture, so entire surface of pastry has been brushed with egg mixture. Sprinkle surface, especially edges with 1 tablespoon Sugar In The Raw Organic White. Bake 13 to 15 minutes or until deep golden brown. Remove to cooling rack to cool completely.
Meanwhile, in 1-quart saucepan, heat cream over medium-low heat just until bubbles form around the edge. In small bowl, beat remaining egg yolks, 1/3 cup Sugar In The Raw Organic White and cornstarch with electric mixer on medium speed or whisk with wire whisk until light in color and creamy. Gradually whisk heated cream into egg yolk mixture, whisking by hand constantly. Return mixture to saucepan. Heat over medium-low heat until mixture thickens and begins to bubble, whisking constantly. Remove from heat; place sheet of plastic wrap directly on surface of mixture. Refrigerate until completely cooled.
When ready to serve, spread cooled filling over tart crust. Space raspberries, blackberries and strawberries randomly over filling. Fill in all spaces with blueberries. Brush tops of fruit with syrup. Sprinkle baked tart with powdered sugar (optional). Cut in squares to serve.
Make-Ahead Tip: The crust and filling can be prepared up to 2 days ahead. Loosely cover the crust and store at room temperature. Cover the filling and refrigerate up to 2 days. Top the tart with about 3 cups of your favorite fresh berries.