Bring a large pot of water to a boil. Place fiddleheads in a steamer basket. Steam for 10 minutes, until tender to the bite. Cool immediately in a bowl with ice water, to preserve the vivid green colour.
Prepare dressing: in a jar, mix ½ cup kefir with the juice of ½ a lemon, 2 TBs each chopped dill and lemon balm and salt and pepper to taste. Close lid, and shake jar for 1 min for the dressing to mix well.