Cook the pasta in a large pot of salted boiling water as the label directs. Drain and toss with the milk in a large bowl; set aside.
Mix the mayonnaise, sour cream and 3 tablespoons chives with the pasta until evenly combined. Season with salt and pepper. Add the lettuce; toss again to coat. Garnish with the reserved bacon and the remaining 1 tablespoon chives. Serve at room temperature. This salad looks gorgeous served in a trifle bowl!