Yield: 1 (13 by 5-inch) tart, 4 to 6 servings
Shop Smart: Buy strawberries of roughly the same size so that when they're "shingled" on the tart, they fit together nicely.
Position a rack in the center of the oven and preheat to 375°F. Line a baking sheet with parchment paper. Roll the pastry into a rectangle about 1/8-inch thick. Cut 2 (3/4-inch wide) strips from a long side. Cut remaining pastry into a 13 by 5-inch rectangle and place on the prepared baking sheet. Brush a 3/4-inch border down 1 long side with water and lay 1 narrow strip on top, pressing gently. Repeat on the other side. (The filling should be thick enough so you don’t need pastry strips on the short sides of the tart to keep the filling from spilling out when the tart is assembled.) Trim any overhang, if necessary. Very lightly roll a pizza wheel along the inside of the strips to score halfway through the base. Brush the top of the strips with milk, taking care not to drip down the sides. Pierce the base all over with a fork, line it with a piece of aluminum foil that extends along the sides of the strips but not over, and weigh foil down with pie weights or dried beans. Use a paring knife to flute the outer edges of the tart by making small cuts an inch apart. Bake until set, about 15 minutes. Remove the foil and weights and bake until light golden brown, about 15 minutes more. Cool on a rack.
Trim the strawberries’ broad tops and put the trimmings in a small saucepan with the rhubarb, sugar, and vanilla extract. Simmer over medium heat, stirring frequently, until fruit is thick and jam-like, about 15 minutes. Add butter and puree with an immersion blender or in a food processor until smooth. Cool. Halve the remainder of the strawberries lengthwise.
To assemble the tart: Spread cooked mixture in the shell. Arrange strawberries in shingled rows down length of the tart.
Stir together jelly and hot water. Brush warm glaze over strawberries. Dust the sides lightly with confectioners’ sugar, slice, and serve with whipped cream.