Rustic Strawberry Rhubarb Tartlets

8 oz strawberries, hulled, coarsely chopped
8 oz rhubarb, thinly sliced
1/2 cup cane sugar
1 tablespoon arrowroot powder
1/2 teaspoon fine lemon zest
1 tablespoon water
big pinch sea salt
1 sheet puff pastry dough

1. Combine the strawberries, rhubarb, sugar, arrowroot, lemon zest, water, and salt in a saucepan. Cook over medium heat, stirring frequently, until rhubarb softens, about 15 minutes. Let cool.
2. Heat oven to 400°F. Lay out the puff pastry dough and cut into 12 equal pieces. (A pizza cutter or dough scraper would work well.) Stretch the dough squares a bit with your hands or roll them out on a lightly floured surface to enlarge them just enough to line the bottom and sides of each muffin cup. Fill the cups with about 1/4 cup filling. Bake for about 25 minutes or until crust is golden brown. Let cool before removing tartlets from the muffin pan. Serve with vanilla ice cream, if desired.