Boozy Caramel French Toast Casserole - Once Upon a Chef

Ingredients

• 1/2 cup (1 stick) unsalted butter, plus more for greasing the pan
• ¾ cup (packed) light brown sugar
• 2 tablespoons light corn syrup
• 1⅓ lbs brioche ((you'll likely need two loaves but you won't use it all))
• 5 large eggs
• 1½ cups half-and-half
• 1 teaspoon vanilla extract
• 3 tablespoons Grand Marnier
• 1 teaspoon orange zest
• ¼ teaspoon salt