1.Cook the pasta in a large pot of salted boiling water. Drain and toss with the milk in a large bowl; set aside.
2.In a large skillet over medium-high heat, heat olive oil. Add the tomatoes, thyme and garlic to the pan and toss until warmed through; season with salt and pepper. Toss the tomato mixture with the pasta.
3.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 remaining 1 tablespoon spring onions. Serve at room temperature.