In a large bowl, whisk together the eggs, milk, maple syrup, vanilla extract, butter, cinnamon, and salt. Set aside.
Place the broken croissants evenly into the bottom of a prepared 9x13 baking dish that has been sprayed with baking spray.
Pour the egg mixture evenly over the broken croissant pieces, making sure to press the croissants into the egg mixture.
Spread the apple pie filling evenly over top of the croissant egg mixture.
Cover and refrigerate at least 4 hours, but overnight is best.
Preheat the oven to 350-degrees (175 degrees Celsius)
Allow the croissant bake to sit at room temperature at least 45 minutes before baking.
Bake the casserole for 90 minutes, or until the center is set, the casserole is puffed, and the top is golden brown.
Allow the casserole to sit for 10 minutes before serving.
Sprinkle with confectioners sugar before serving and additional maple syrup if desired.
Notes
Make this casserole in advance and refrigerate at least 4 hours (overnight is preferred) for best flavor.Store any leftovers in the refrigerator in an airtight container for up to 5 days.