Chop lettuces into wide strips. Place in a serving bowl.
To make vinaigrette, whisk oil, vinegar, lemon juice and mustard until combined; add salt and pepper to taste. To make creamy chive yogurt, combine sour cream, yogurt and chives; add salt and pepper to taste.
To make croutons, cut bread into small cubes. Melt herb butter in nonstick pan over medium heat. Add bread cubes; cook until golden brown on all sides, taking care butter does not burn. Set aside; keep warm.
Drizzle vinaigrette over lettuce. Toss to coat. Sprinkle with spring onions. Spoon on dressing; top with croutons.