Melt 1 tablespoon of the butter in a small saucepan over medium heat. Add the shallot and sauté until softened, 1-1/2 minutes. Sprinkle with the allspice, cinnamon and ginger.
Add the pomegranate and orange juices, increase the heat to medium-high and bring to a rapid simmer. Cook, uncovered, until reduced to about 1/2 cup, 6 to 8 minutes.
Add the lemon zest and remaining tablespoon of butter and stir until the butter has melted. Season to taste with salt and pepper.