1. Preheat to 375 degrees F. Line a baking sheet with parchment paper.
2. Roll pastry into a rectangle 1/8-inch thick and at least 13 by 8-inch in dimension. Cut two 13 by 3/4-inch- wide strips from dough. Trim remaining pastry into a 13 -by 5-inch rectangle and place on prepared baking sheet. Brush long edges with water and press on strips to create a border. Lightly score dough inside border. Brush top of strips with milk, do not allow drips down sides. Prick base all over with a fork.
3. Line dough aluminum foil extending along sides but not covering strips. Flute edges using tip of a paring knife to make small cuts an inch apart. Place pie weights on foil. Bake on middle rack of oven until set, about 15 minutes. Remove foil and weights and bake until light golden brown, about 15 minutes more. Cool on a rack.
4. Trim strawberries' broad tops and place trimmings in a small saucepan with 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 remaining strawberries lengthwise.
5. Spread cooked rhubarb mixture in shell. Arrange strawberries, slightly overlapping, in 3 rows over filling.
6. For glaze: Stir jelly and hot water together. Brush over strawberries. Dust tart sides lightly with confectioners' sugar. Slice and serve with whipped cream.
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