Step 1

Blend anchovies, garlic, mayonnaise, sour cream, basil, parsley, tarragon, 1 Tbsp. lemon juice, and 4½ tsp. oil in a blender until smooth with only a few flecks of green; season dressing with salt.

Step 2

Combine lettuce, radishes, and remaining 1 Tbsp. plus 1 tsp. lemon juice in a large bowl, drizzle with oil, and season with salt; toss to combine.

Step 3

Top salad with a few spoonfuls of dressing; reserve remaining dressing for another use (like a turkey sandwich!).

Step 4

Do Ahead: Dressing can be made 1 day ahead. Cover and chill.