Preheat oven to 400F. Line a baking sheet with parchment or a Silpat; set aside.

In a large bowl, whisk together flour, sugar, baking powder, and salt.

Cut in cold butter using a pastry cutter or two forks until the mixture resembles coarse wet sand with some larger pea-sized clumps.

In a small bowl, whisk egg, sour cream, vanilla, and zest until smooth.

Pour wet mixture over dry ingredients and fold gently until just combined; the dough will be shaggy and wet.

Gently fold in mixed berries.

Lightly flour a work surface. Turn dough out and knead into an 8-inch round. If dough is too sticky, sprinkle with additional flour.

Cut into 8 wedges with a knife.

Transfer wedges to baking sheet, spacing at least 2 inches apart. Sprinkle each with turbinado sugar if desired.

Bake for 18 minutes or until lightly golden.

Allow to cool slightly on baking sheet, then move to a wire rack. Make the glaze by whisking confectioners' sugar and cream until smooth, adding more liquid if needed.

Drizzle glaze evenly over warm scones before serving.