01 - 
                Preheat the oven to 375°F (190°C) and line a baking sheet with parchment paper.
              
              
              
                02 - 
                Spread Dijon mustard and mayonnaise on the inside of each croissant half, if using.
              
              
              
                03 - 
                Layer two slices of ham and two slices of cheese inside each croissant. Close the croissants and place them on the prepared baking sheet.
              
              
              
                04 - 
                Lightly brush the tops of the croissants with melted butter.
              
              
              
                05 - 
                Bake for 12-15 minutes, or until the cheese is melted and the croissants are golden brown.
              
              
              
                06 - 
                Remove from the oven and serve warm.