Lamb - Ground
To make the meatballs:
In a small non-stick skillet cook onion and garlic in oil over moderately low heat, stirring, until softened. Transfer mixture to a bowl and stir in mint, salt, allspice, and cinnamon. Add lamb, bread crumbs, egg, and currants and combine well. Form level tablespoons of lamb mixture into 1 1/4-inch meatballs, arranging on a tray as formed.
In a small bowl roll half of meatballs, 1 at a time, in black sesame seeds until coated, transferring to a rack set in a shallow baking pan. Coat remaining meatballs with white sesame seeds in same manner, transferring to rack. Meatballs may be prepared up to this point 1 day ahead and chilled, covered loosely.
Preheat oven to 450°F.
Bake meatballs in upper third of oven 8 to 10 minutes, or until golden and just cooked through.
To make the yogurt dip:
In a fine sieve set over a bowl drain yogurt, covered and chilled, 3 hours. Discard whey in bowl and transfer yogurt cheese to bowl. Yogurt cheese may be made 2 days ahead and chilled, covered.
Into yogurt cheese stir mint and salt. Makes about 1 1/2 cups.