Preheat your oven to 350 degrees. Thoroughly grease and flour 10 ramekins or mini cake pans.
In a medium bowl, whisk together the flour, baking powder, baking soda, and salt. In another small bowl, combine the buttermilk, clementine juice, vanilla, and orange liqueur. Set both of these mixtures aside.
In a large bowl, cream the butter and sugar together for 3-5 minutes, or until light and fluffy. Beat in the eggs one at a time, followed by the clementine zest. Add the flour and buttermilk mixtures alternately to the batter, starting and ending with the flour. Divide the batter evenly among the ramekins, smooth the tops, and bake for about 22 minutes, or until a toothpick comes out clean. Allow the cakes to cool completely.
Make the glaze by combining powdered sugar, 2 teaspoons orange liqueur, 1 teaspoon water, and a drop of vanilla. Glaze the tops of the cakes and top with the clementine segments and lemon zest, if using.