Prepare the Filling

1. Preheat Oven: Preheat your oven to 400°F (200°C).
2. Roast the Squash: Toss the diced butternut squash with olive oil, salt, pepper, and thyme. Spread it on a baking sheet and roast for 25-30 minutes, or until tender and slightly caramelized. Remove from the oven and let cool slightly.
3. Mix Filling: In a mixing bowl, combine the roasted butternut squash, crumbled feta cheese, eggs, and heavy cream. Mix until well blended.

Assemble the Tartlets

1. Prepare Pastry Shells: Place the pre-made pastry shells on a baking tray.
2. Fill the Shells: Spoon the butternut squash and feta mixture into each pastry shell, filling them about three-quarters full.

Bake the Tartlets

1. Bake: Place the filled tartlets in the preheated oven and bake for 20-25 minutes, or until the filling is set and the tops are lightly golden.
2. Cool: Remove from the oven and let cool for a few minutes before serving.