1. Preheat oven to 425 degrees.
2. In the bowl of a food processor, combine the flour, 2 tablespoons of sugar and salt.
3. Add butter and pulse until the mixture resembles coarse crumbs.
4. Add water until the dough just starts to come together. (Test the texture by pinching the dough between your fingers. If it holds together, it’s ready. If the dough is crumbly, add water a tablespoon at a time and pulse until the dough holds together.)
5. Transfer dough to a floured work area and form it into a ball. Cut into fourths. (Actually, Lucy’s recipe says to cut into eigths, but I wanted 2-person crostatas.)
6. Form each quarter into flat discs and wrap them individually in cellophane. Refrigerate dough for about 20 minutes.
7. Meanwhile, prepare your fruit and toss the rhubarb and berries in a bowl. Add the remaining ¾ cup sugar and cornstarch. Toss together - syrup will form.
8. On a lightly floured surface, roll out each disc of dough to a circle about 1/8” thick. Transfer dough to a lipped baking sheet lined with parchment paper (you’ll thank me for this). Mound a quarter of the fruit filling into the center of the dough and fold the edges over the fruit, pleating as you go. Repeat for additional pastry discs and fruit.
9. Refrigerate crostatas for 10 minutes.
10. With a pastry brush, lightly sweep cream over the pastry and sprinkle with turbinado sugar.
11. Bake for 23-25 minutes.
12. Heat jam in a microwave for 30 seconds or so. With a pastry brush, dab the strawberries and rhubarb with the jam to give it that glistening, jewel-like effect.
13. Can be served warm or at room temperature.