Prepare baking sheet with parchment paper, set aside. Preheat broiler.
In medium skillet add butter and melt over heat.
Once butter is melted, whisk in flour until mixture is smooth. Slowly whisk in milk until mixture starts to thicken. Remove from heat and whisk in ½ cup swiss cheese, thyme leaves, nutmeg, salt and ground pepper.
Lay out bread and spread each slice with ½ tablespoon Dijon mustard; top with 1 tablespoon swiss cheese sauce.
Top 2 slices of bread with 4 slices bacon and 2 tbsp shredded swiss cheese.
Place bread slices on baking sheet. Broil in oven until cheese is melted.
Remove from oven and top with remaining slice of bread, cheese sauce side down. Top each sandwich with equal parts swiss cheese sauce and remaining shredded swiss cheese.