How to Make It
Preheat oven to 400°.
Starting at the outermost edges, cut most (but not all) of the way through each apple half at 1/8-inch intervals. Place apple halves, cut sides down, in an 8-inch square glass or ceramic baking dish coated with cooking spray. Combine 2 tablespoons sugar, 2 tablespoons butter, and 1 teaspoon cinnamon; brush mixture evenly over apple.
Cover pan with foil; bake at 400° for 20 minutes. Remove foil. Bake at 400° for 10 minutes or until apples are tender. Remove pan from oven; cool 10 minutes.
Meanwhile, lay out puff pastry on a sheet pan lined with parchment paper. Using a spatula, place each cooled apple on the puff pastry, two in a line.
Combine remaining 6 tablespoons sugar, remaining 3 tablespoons butter, remaining cinnamon, oats, flour, and salt.
Carefully fan open apple halves. Spoon oat mixture evenly over apples. Using a pastry brush, brush the egg on the crust and sprinkle with sugar. Bake at 400° for 15 minutes until pasty is golden.
Turn broiler to HIGH (leave pan in oven); broil 2 minutes but check to make sure the crust does not burn. Serve with ice cream.