Apple Raspberry Cardamom Tarts with Buttermilk Pastry

Steps

1. Make the pastry first: whisk the flour, the salt and 20 g of the sugar (about one-eleventh of the total) in a large bowl.
2. Add the cold butter and rub or cut it in until the pieces range from peas to flattened almonds.
3. Drizzle in the cold buttermilk and toss with a fork until the dough holds together when squeezed; add no other liquid.
4. Divide the dough into four equal pieces, flatten each into a disk, wrap and chill for 1 hour.
5. While the dough chills, toss the apple with the orange juice in a large bowl.
6. In a small bowl, whisk 180 g of the sugar (most of it, leaving 20 g for the top) with the cornstarch, lemon zest, cardamom and cinnamon; toss this mixture with the apples.
7. Gently fold in the raspberries so they stay mostly whole.
8. Roll two dough disks into 12-inch rounds and fit them into two 9-inch tart or pie pans, leaving the overhang.
9. Divide the fruit filling evenly between the two crusts, scraping in the juices.
10. Roll the remaining two disks into 11-inch rounds and lay one over each tart as a full lid; trim, fold the edges under and crimp to seal.
11. Cut four short vents in each lid and chill the tarts for 15 minutes; meanwhile heat the oven to 400°F (200°C) with a rack in the lower third and a baking sheet on it.
12. Brush the lids with the beaten egg and sprinkle evenly with the remaining 20 g of sugar.
13. Set the tarts on the hot baking sheet and bake 20 minutes, then lower to 375°F (190°C) and bake 35 to 40 minutes more, until the crust is deep golden and juices bubble thickly through the vents; tent edges with foil if they brown too fast.
14. Cool on a rack for at least 3 hours so the filling sets, then cut each tart into 6 slices.