Heat the butter in a skillet over medium heat. Add in the sourdough pieces with a pinch of salt. Cook, tossing often, until they are golden and toasty and crisp. Turn off the heat.
Place the romaine in a large bowl and toss with a big pinch of salt and pepper. Drizzle with a few tablespoons of the caesar dressing. Add in the finely grated parmesan. Toss the lettuce well so everything is coated. Add in the cooked pasta and toss it well, adding more dressing if you would like. Toss until everything is combined and well coated.
Top with the shaved parmesan and the sourdough croutons. Serve with extra dressing and more parmesan cheese. You can use this as a base salad for chicken, steak, salmon, chickpeas, etc.
To make the dressing, add the garlic, yogurt, parmesan, mustard, vinegar, anchovy paste, lemon juice, salt and pepper to a food processor or blender and blend until pureed. With the processor still on, stream in the olive oil until a creamy dressing forms. (This may make more dressing than needed, but you can store it sealed in the fridge for about 3 to 4 days and stir well before using.)