1 head of cauliflower (about 1-1/2 pounds, cut into medium florets, 1 inch at their widest point)
1 small head of garlic
3 1/2 tablespoons olive oil (divided)
  coarse (kosher) salt
  freshly ground pepper
1 cup thinly sliced leeks
1/4 cup white wine
4 cups chicken stock
2 teaspoons chopped fresh thyme
2/3 cup half & half or light cream
  white or black truffle oil (as garnish)