For a richer flavor, consider using Gruyère or Emmental cheese instead of Edam. If white asparagus is unavailable, green asparagus can be substituted, although the flavor will be slightly different. To save time, the asparagus can be poached ahead of time and stored in the refrigerator until ready to use. Be sure to reheat slightly before assembling the toasts. A drizzle of high-quality olive oil over the finished toasts adds a lovely touch.