Line a large baking sheet with parchment paper or a silpat baking matt. Set aside

Whisk together flour, sugar, baking soda, baking powder and salt in a bowl. Using a cheese grate, grate frozen butter into flour mixture and cut with a pastry blender or two knives until butter is in small pieces. Set aside.

In a small bowl, whisk together egg, heavy cream, vanilla, lemon juice and lemon zest. Drizzle over flour and butter mixture and whisk together until just combined. Add blueberries and white chocolate chips and gently stir, being careful not to overmix the blueberries.

Flour your hands. Remove the dough from the mixing bowl and place on a floured work surface. Roll into a rectangle, about 1 inch thick. Cut into 8 triangles; pull the triangles apart from each other and brush with heavy cream and sprinkle with sugar. Place in the refrigerator for at least 30 minutes.

Preheat oven to 400 and bake for 20-22 minutes. Use a toothpick inserted in center to check if it's done. If toothpick comes out clean, it's done. Let cool on pan for 5 minutes.