Tarragon is a great spring and summer herb that provides a spicy addition to the dressing.
For the dressing:
For the salad:
Add the vinegar, salt, sugar, tarragon, and mustard to a medium stainless steel bowl. Whisk to combine. Add egg yolk and whisk until smooth.Continue to whisk as you add the olive oil in a slow, steady stream until it is completely incorporated. Add the garlic and refrigerate in a sealed non-reactive container until ready to use. It will keep for up to 1 week in the refrigerator.
Tear lettuce and radicchio into bite-sized pieces into a medium stainless steel bowl. Toss with your hands until lettuces are combined well. Add dressing to taste and toss again using your hands to avoid bruising the lettuce. Divide equally between 4 chilled salad bowls and serve with freshly ground black pepper.