Combine the tequila, simple syrup, lime juice, bitters and ice in a cocktail shaker and shake for 10 seconds. Serve straight up or on the rocks with a lime wedge for garnish.
Spiced Simple Syrup:
Combine the sugar, 1 cup water, allspice, cloves, cinnamon and ginger in a small saucepan. Bring to a boil and cook until the sugar is completely melted. Remove from the heat and let steep for 1 hour. Strain into a small bowl, cover and refrigerate until cold.