In the jar of a blender, combine all the ingredients through the garlic. Blend until smooth. While the blender is running, add the oil in a steady stream. Turn off the blender and add the feta and pulse the blender a few times (more if you want a creamier consistency). Whisk in the herbs. If possible, refrigerate for at least an hour before serving. Use as a marinade for chicken, lamb, or flank steak or drizzle over a Greek salad.