Pai Apel yang Mudah

Bahan-bahan (2 porsi)

• 1 sheet frozen puff pastry ((a package comes with 2 sheets))
• 1 Fuji apple
• 1 Tbsp unsalted butter ((melted))
• 3 Tbsp sugar
• 1 large egg yolk
• 1 –2 sprigs rosemary ((fresh; optional))