Preheat oven to 400°F (205°C) and line a baking sheet with parchment paper. Remove the puff pastry from its package and let sit at room temperature for 10 minutes while you prep the other ingredients.

Quarter and core the apples, then slice into thin wedges. Slice the onion into very thin crescent strips. Pluck the rosemary leaves from their stems.

Once the puff pastry has thawed enough to handle, unfold it and cut the dough into 12 equal squares. Place the squares on the prepared baking sheet, then layer the apple slices across each, fanning them across the entire surface. Top with the onion slices, then the rosemary leaves, and season with salt, pepper, piment d’espelette or paprika, and sugar. Tuck the butter cubes between slices of apple and onion, distributing evenly across the tarts. Bake for 35 minutes, or until the puff pastry is cooked through, golden and crispy on the bottom.

While the tarts bake, prepare the glaze by combining the preserves and brandy in a small pot. Heat over medium and keep warm. When the tarts are done, remove them from the oven and gently dab the glaze over each one, then garnish with additional rosemary. Allow to cool for 10 minutes and serve