Preheat oven to 425˚F (220˚C). In a mixing bowl or bowl of stand mixer, whisk together flour blend, 1/4 cup (60 mL) of the sugar, baking powder, xanthan gum and salt until blended. Using fingers, 2 forks or a pastry cutter, cut in butter until thoroughly combined. Stir in cranberries.
In a separate bowl, beat together buttermilk, egg, lemon zest and vanilla until blended. Pour buttermilk mixture over flour mixture; mix well until wet dough forms.
Transfer dough to a lightly floured surface. Using floured hands, press and shape dough into a ball; flatten into 7-in. (18 cm) wide disc. Transfer dough to a baking sheet lined with parchment paper. Cut disc in half; cut each half into 5 wedges. Spread wedges about 3 in. (8 cm) apart. Sprinkle remaining sugar over top. Bake until golden brown, 12 to 13 min. Let cool in pan on rack for 10 min. before serving.