1. Lightly crush cinnamon sticks, star anise, allspice, and cloves with mortar and pestle. Place in resealable plastic bag, and pound with rolling pin. Transfer to large saucepan, and add sugar and 8 cups water. Bring mixture to a boil, and simmer until sugar dissolves. Remove from heat, add coffee, and let steep 5 minutes.
2. Meanwhile, warm milk in small saucepan, and whisk until frothy.
3. Strain coffee through fine sieve or coffee filter into pitcher. Stir in coffee liqueur (if using). Serve with frothed milk.