Step 1

Combine the lemon and 4 cups water in a large bowl. Place the sliced apples in the water to keep them from browning.

Step 2

Melt butter in a large skillet over medium heat. Drain water from apples, and place them into the hot skillet. Cook and stir for about 2 minutes. Add brown sugar, and cinnamon, and cook, stirring, for 2 more minutes. Stir together cornstarch and 1 tablespoon water. Pour into the skillet, and mix well. Cook for another minute, or until sauce has thickened. Remove from heat to cool slightly.

Step 3

Preheat the oven to 400 degrees F (200 degrees C).

Step 4

Unfold puff pastry sheets, and repair any cracks by pressing them back together. Trim each sheet into a square. Then cut each larger square into 4 smaller squares. Spoon apples onto the center of each squares. Fold over from corner to corner into a triangle shape, and press edges together to seal. Place turnovers on a baking sheet, leaving about 1 inch between them.

Step 5

Bake for 25 minutes in the preheated oven, until turnovers are puffed and lightly browned. Cool completely before glazing.

Step 6

To make the glaze, mix together the confectioners' sugar, milk and vanilla in a small bowl. Adjust the thickness by adding more sugar or milk if necessary. Drizzle glaze over the cooled turnovers.