- 2½ cups all-purpose flour
- 1 teaspoon cane sugar, plus 1 teaspoon for sprinkling
- 1 teaspoon kosher salt
- 2 sticks butter, freezer-cold and chopped into small cubes
- ¼ cup ice water
- ¾ pound rhubarb, rinsed, ends trimmed, cut into ¼-inch pieces
- 2 pints fresh strawberries, rinsed and hulled, cut into ¼-inch pieces
- ½ cup cane sugar
- Zest of 1 orange
- ¼ cup orange juice
- Pinch kosher salt
In a food processor, pulse the flour, sugar, and salt to combine. Add the cold butter and pulse 5 to 7 times, until the butter mixes with the flour to form pea-size crumbs. In a slow stream, add the ice water while pulsing, stopping once the dough holds together. To test the dough, unplug the food processor, open the lid, and press some dough together. If it holds together, it’s ready. If it still crumbles, add a bit more ice water as you pulse a few more times. You may use slightly less or slightly more than cup of water. Separate the dough into two mounds, then flatten each to form a disk. Cut the plastic wrap in two between the disks, and wrap each. Refrigerate for at least 20 minutes to let it firm up.
In a large bowl, carefully mix together the rhubarb, strawberries, sugar, orange zest, orange juice, and salt. Cover with plastic wrap, and let the flavors blend, at least 15 minutes.
On a lightly floured surface, cut each dough disk into four. Chill the rest as you roll each one out. Roll from the center to the edge, turning an eighth turn with each pass of the rolling pin, until the dough is 1⁄8 inch thick. (They don’t have to be perfect circles. Patch any large tears with dough pinched from the edge.)
Line two baking sheets with parchment paper, and lay the rolled pastry 2 to 3 inches apart from each another. Spoon mounds of the fruit mixture into the center of each pastry, dividing the filling evenly and leaving a 1-inch border around the edge. Assemble one set of tarts at a time, leaving the other batch of pastry in the refrigerator.
Gather the pastry, making pleats onto the piled fruit. Lightly brush water in between the folds to press the pastry together and keep it in place. If the dough becomes flabby, it needs to be rechilled. Once you have filled and crimped all the tarts, refrigerate them for at least 1 hour before baking.
Preheat the oven to 400°. Very lightly brush the edges of the pastry with water, and sprinkle with reserved 1 teaspoon of sugar. Bake for 30 minutes, or until the crusts are golden, then lower the temperature to 375° and bake for 10 to 15 minutes, until the juices bubble and the crust is deeply golden. Transfer the tarts to a wire cooling rack to cool.
Remove the tarts when they can be easily handled, and enjoy them warm. Store leftover tarts at room temperature, wrapped loosely in foil, for 2 days