Preheat the oven to 350°F and spray the muffin pan with nonstick spray.

Wash the apples, cut them in half lengthwise, and remove the core.

Slice the apples thinly widthwise, keeping the open side of the apple down.

Put the apple slices in a bowl and add the lemon juice.

Add 1–2 teaspoons of sugar and a small pinch of cinnamon to the apples and mix until well combined. Set aside the remaining sugar and cinnamon.

Melt the butter in the microwave and brush it onto one side of each puff pastry sheet.

Mix the remaining sugar and cinnamon together and spread it over the puff pastry on the buttered side.