Smooth the goat cheese with the milk, then stir in the garlic, thyme, and a little pepper. Broil the bread just until the tops are lightly colored, then spread the cheese mixture thickly over the untoasted side and set aside. Toss the salad greens with a pinch of salt, then with the vinaigrette, and arrange on individual plates. Broil the croutons until the cheese begins to slump and bubble, about 3 minutes. Sprinkle on the thyme, then set the cheese toasts right on top of the greens. Grind black pepper over the top and serve.