In a bowl, whisk together the flour, sugar, baking powder, and baking soda. Using large holes of a grater, grate frozen butter into the flour. Use fingers to work in the butter until it resembles a coarse meal. Stir in white chocolate chips.
In separate bowl, whisk together sour cream, eggs, and vanilla until smooth and incorporated.
Use a fork to stir sour cream mixture into flour mixture until large clumps form. Gently stir in cranberries. Use hands to form dough into two even sized balls.
If dough is sticky and needs to firm up a bit, wrap dough balls tightly and chill until it's easier to work with, about 20 to 30 minutes.
Meanwhile, line baking sheets with parchment paper. Set oven to 400 degrees F.
On a lightly floured, flat surface, pat each dough ball evenly into an 8 inch circle, about ¾ inch thick each. Cut each circle into 8 triangle wedges. Place triangles on lined baking sheets, 1 inch apart.
To make the egg wash, lightly beat the egg and water together. Brush the egg wash on top of each triangle. Sprinkle tops with coarse sugar.
Bake about 14-17 minutes or just until tops are light golden.