Butter Lettuce with Mustard Vinaigrette

2 heads butter lettuce 

3 1/2 Tbs. extra-virgin olive oil 

1 1/2 Tbs. red wine vinegar 

1 tsp. Dijon mustard 

Salt and freshly ground pepper, to taste 

1 Tbs. chopped fresh chives 

1 Tbs. chopped fresh tarragon  

1 Tbs. chopped fresh flat-leaf parsley