How to Make It
Preheat oven to 400°. Unfold 1 pastry sheet, and roll to a 9- x 12-inch rectangle on a lightly floured surface. Cut pastry into 9 (4- x 3-inch) rectangles. Brush edges of rectangles with a small amount of egg whites. Stir together apple butter and thyme leaves. Spoon about 1 tsp. apple butter mixture into center of each rectangle. Sprinkle each with about 1 Tbsp. cheese. Fold 2 opposite corners together, and pinch to seal.
Gently transfer to a parchment paper-lined baking sheet. Brush pastries with egg whites, reserving remaining egg whites for second batch; sprinkle each pastry with about 1/2 Tbsp. cheese.
Bake at 400° for 20 to 25 minutes or until puffed and golden brown. While first batch bakes, repeat procedure with remaining pastry sheet, egg whites, apple butter mixture, and cheese. Serve immediately.