Prep the butter: grate the frozen butter onto a plate (I recommend cutting the stick in half first, then grate one half at a time). If you forgot to freeze the butter, cut it with a sharp knife into small cubes. Stick it back in the fridge or freezer for now.
To a big bowl: Add the all purpose flour, whole wheat flour, sugar, lemon zest, salt and baking powder. Whisk together. Then add in the grated/cut butter and use a pastry cutter, two forks or your fingers to incorporate the butter with the dough so it comes together in pea-sized crumbs. Place in the fridge.
To another bowl: Add the heavy cream, egg and vanilla and mix to combine.
Add the wet ingredients to the dry. Add the blueberries and mix with a wooden spoon until you don't see any big pockets of flour. The dough will be thick and sticky.
Turn the dough onto a big clean cutting board (easier clean up) and try to shape the dough into a ball. If the dough seems dry, add 1-2 tablespoons of heavy cream. Add a sprinkle of flour if it's really sticky. Press the dough into an 8-inch disc (I just eyeball it) then, using a sharp knife, cut the disc into 8 wedges. Transfer the wedges to a plate. Brush heavy cream on top of the scones and freeze for 10-15 minutes.
Preheat the oven to 400 F and prepare a baking sheet with cooking spray, parchment paper or a baking silicone mat while your dough chills.
Arrange the scones on the sheet pan so they have some space and bake for 20-25 minutes, until the tops are golden. Let them cool completely before storing in a container!