1. To make the pastry, pulse the flour, butter, and salt in a food processor until the mixture resembles coarse bread crumbs. Add the egg and pulse until it clumps together. Gather into a disk, wrap in plastic wrap, and refrigerate for 30 minutes.

2. Divide the pastry into six portions, and roll out each into a 1/8 in (3mm) thick round. Line each pan with a round, trimming the excess dough. Prick the dough with a fork. Refrigerate for 30 minutes.

3. Preheat the oven to 400°F (200°C). Line the tart pans with parchment paper and fill with baking beans. Bake for 10 minutes. Remove the paper and weights and bake until lightly browned, about 10 minutes. Remove from the oven, and reduce the temperature to 375°F (190°C).

4. Mix the créme fraîche, egg yolks, dill, horseradish, capers, and lemon juice and zest. Add the trout and season with salt and pepper. Divide among the tart pans.

5. Bake about 15 minutes, until the filling sets. Cool 5 minutes, remove sides of the pan, and serve hot.