Preheat oven to 350°F. Prepare 1 1/2 muffin pans by lining with cupcake liners.
In a medium bowl, whisk together flour, baking soda and salt, and set aside. Zest the clementine/mandarin oranges and Meyer lemon and stir into the flour mixture. Set aside the citrus.
In the bowl of an electric mixer, cream butter and sugar together. Add vanilla and egg, mix well. Squeeze the juice of the citrus and add 1/4 cup of the citrus juice into the buttermilk. Add the buttermilk and flour mixture in batches, alternating. Stir in the cranberries.
Spoon the batter into the muffin pans, filling to about 2/3 full. Bake for about 18 minutes, or until golden and a toothpick inserted in the center comes out clean and the cake is springy to the touch.