These are delish. It's a little more time consuming but they are well worth it. I found a recipe online (see link below) and adapted it to my liking and with items that I had on hand.
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2 T butter
3 T flour
1 cup hot milk
1/2 t black pepper
3 c shredded swiss cheese
4 croissants, cut in half
1/4 lb of honey ham
1. Preheat oven to 400F.
2. Toast croissants 4 minutes on one side and 2 minutes on the other.
3. Melt butter in a sauce pan over medium heat.
4. Whisk in flour.
5. Continue whisking while adding in the hot milk.
6. Once sauce has thickened, remove from heat and stir in 1 1/2 cups of shredded swiss until melted.
7. Prepare croissants by spreading with honey mustard and layering the honey ham and half of the remaining swiss.
8. Then top the croissants with remaining swiss and the cheese sauce.
9. Bake for 5 minutes.
10. Turn on broiler and brown the cheese for an additional 3 minutes.
Recipe adapted from: http://savuryandsweet.com/2011/04/26/croque-monsieur-my-way/