Preheat the oven to 350F degrees. Spray a 10 x 7 inch oval baking dish with nonstick cooking spray (or just coat in butter).
Arrange croissants in the baking dish so as to know where to place them after tossing in the egg mixture.
In a small bowl, beat heavy cream, milk, thyme, eggs, salt and pepper together. Roll croissant slices into the egg mixture (one by one) and put back in the baking dish.
Pour rest of egg mixture over the tops of the croissants in the baking dish.
Top evenly with cubed mozzarella and sliced ham (or prosciutto). Tuck the ham down gently in between the croissant pieces.
Cover the dish with foil, place on a baking tray and bake for 30 minutes.
Remove foil and bake for another 5 - 10 minutes or until croissants are golden on top (don't remove the foil if you prefer your croissants to stay extra soft on top.)
Remove and serve immediately with honey and more fresh thyme if desired.
Notes
This casserole can be prepared the night before, covered then stored in the refrigerator until ready to bake.
Other cheese options include: cheddar, brie or parmesan.
Make it vegetarian by adding mushrooms instead of ham.
Bacon can be used but it should be pre-cooked before using in this dish or else it will produce too much grease.
I have only tested this with full fat cows milk so I can't say how it would turn out using milk alternatives.