- Preheat the oven to 350 degrees. Lightly grease a 9 x 13-inch baking dish with butter.
- Break up the croissants into small pieces and place in the baking dish. Lightly toast the croissant in the oven for 5-8 minutes. Remove and set aside.
- In a large bowl, whisk together milk, eggs, and honey mustard. Pour the mixture over top the toasted croissants in the casserole dish. Place pieces of ham and havarti between and among the croissant pieces. Sprinkle shredded swiss and rosemary on top.
- Cover the dish and bake for 25-30 minutes, then remove the foil, and continue baking for 15 minutes, until the croissants are golden brown.