Put the onion, orange juice, potato, butter, cumin, bay leaves, and 3 cups water in a large (at least 4-quart) saucepan. Cover, bring to a boil over high heat, and reduce to a simmer. Cook until a skewer easily pierces the potato, 15 to 20 min. Add the tomatoes with their juices and the orange zest. Bring to a boil, reduce the heat to maintain a steady, low simmer, and cook, uncovered, until the potato chunks are falling apart, another 20 min. Discard the bay leaves. Purée the soup with an hand blender, stand blender, or food processor. Strain through a medium sieve; discard the contents of the sieve. Season with salt and pepper. If not serving immediately, let cool completely before refrigerating or freezing. Heat gently, adjust the salt and pepper as needed, garnish with the chives, and serve.
Strain through a sieve before serving.
Photo: Scott Phillips