Preheat oven to 350℉. Lightly spray 9×13-inch baking dish with cooking spray and set aside.

Add 1 pound hot ground pork sausage to large skillet over medium heat. Brown and crumble sausage completely, about 7-8 minutes. Drain excess grease and set aside.

Slice 8 to 10 full-size croissants in half horizontally, then tear into large pieces, about 2 to 3 inches each. Add torn croissants to prepared baking dish.

In large mixing bowl, whisk together 6 large eggs, 1½ cups half and half, 1 teaspoon Dijon mustard, 1 teaspoon salt, ¼ cup pure maple syrup, pinch of cinnamon, and half of sliced green onions until smooth and well combined. Reserve remaining green onions for garnish.

Scatter cooked sausage evenly over croissants in baking dish. Pour custard mixture over everything, gently pressing croissants down to help them absorb custard.

Sprinkle 2 cups shredded cheddar cheese evenly over top of casserole.

Bake for 40-45 minutes, until croissants are golden brown and cheese has crisped up. Check at 30-minute mark -- if croissants or cheese are browning too quickly, tent loosely with aluminum foil for remaining bake time.

Remove from oven and let cool 5-10 minutes. Garnish with reserved green onions before serving.