Step 1Stir together feta cheese and enough crème fraîche to make a nice spread. Chop enough of 1 or 2 of your chosen herbs to yield 2 tablespoons. Snip most of the chives into 1/8- to ¼-inch pieces. Stir the chopped herbs and chives into cheese. Thinly slice or julienne the radishes. Cut the halvah into thin slices.
Step 2Toast the bread. Divide the cheese mixture among the slices, spreading it over each of the toasts. Lay several of the largest whole leaves from your selection of herbs over the cheese along with any remaining whole chives as desired. Arrange several slices of halvah over the herbs. Top generously with radishes, mint and any other small herb leaves. Cut the tartines in half and serve.