For Pastry

1. Combine flour, salt, and butter in food processor or pastry cutter, until you get a bread crumb-like consistency.
2. Add egg and combine until dough comes together into a ball. If it’s dry, add ice water, 1 to 2 teaspoons at a time until it comes together.
3. Grease a 10″ (25cm) metal tart pan with removable bottom, with butter (from the tart filling).
4. Sprinkle bottom & sides evenly with the sugar.
5. Tip dough onto clean work surface and knead lightly for a few seconds.
6. Using a rolling pin on a slightly floured surface, roll the dough out.
7. Transfer to greased tart pan, pressing it up the sides to adhere. Prick bottom with a fork.
8. Cover loosely with a kitchen towel, and let rest in fridge for 30 minutes (or up to a day).

For Filling

1. Preheat oven to 425°F / 220°C.
2. Halve and pit the plums. If they’re very small (1″), just leave them as halves, otherwise go smaller.
3. Arrange the plums skin side down on the dough in a circular pattern, starting from the outside, overlapping slightly. They will shrink slightly as they bake.
4. Bake for 20 minutes.
5. While baking, heat apricot jam over low heat. Strain through a fine-mesh sieve to remove skins.
6. Remove tart from oven, leaving the oven on. Remove the sides of the tart pan.
7. Using a pastry brush and the apricot jam, glaze the sides of the tart, outside and in, and the top of the fruit.
8. Return to oven until darkly caramelized, 5-10 minutes. Transfer to a rack to cool completely.