Gather ingredients and preheat the oven to 400°F (200°C). Line a baking sheet with parchment paper and set out two 6-ounce ramekins.

Place puff pastry sheet on a work surface to thaw for 5 minutes. Cut 2 rounds of dough to match ramekin diameter and transfer to a baking sheet. Prick each round with a fork.

Bake until puffed and golden brown, about 15 minutes. Let cool and press down lightly to deflate.

Increase oven temperature to 425°F (220°C). Mix sugars, cinnamon, and salt in a bowl.

Use 1 1/2 teaspoons butter to grease ramekins. Distribute sugar mixture evenly, reserving 1 1/2 teaspoons.

Peel apples into ribbons using a potato peeler, and soak ribbons in water mixed with lemon juice.

Assemble each tart by coiling apple ribbons to the diameter of the ramekin and placing them inside on the sugar mixture.

Dot remaining butter over apples. Sprinkle reserved sugar mixture and place pastry rounds on top, pricked side down.

Bake until browned and juices bubble, about 30 minutes. Let cool for 10 minutes before serving.