I thought I knew my harissa after nearly two decades of making it from scratch. Then I tasted a spoonful of rich, wine-dark paste from an unmarked jar that arrived on my doorstep from brothers Mansour and Karim Arem. They were on the verge of launching Zwita, a company focused on celebrating their Tunisian heritage. Whereas western cooks and food writers are familiar with many of the food traditions of nearby Morocco, we've largely neglected to learn anything about Tunisia or its culinary history.