Grate the frozen butter using a box grater. Return the grated butter to the freezer to stay cold as you prepare the rest of the ingredients.
In a large bowl, whisk to combine the flour, baking powder, cinnamon, lavender and salt. Add the grated butter to the flour mixture and stir/toss the butter into the flour mixture with a fork until the butter is coated with flour and is about the size of peas.
In a small bowl, whisk to combine the heavy cream, egg yolk, brown sugar and granulated sugar, lemon zest, and vanilla extract. Pour the wet ingredients over the flour/butter mixture and stir with a spatula til slightly combined.
Add the white chocolate chips and blueberries and stir until just combined. Do not overmix. Dough shouldn't be too dry and should be somewhat sticky, but not too sticky. If dry there are some dry spots, add a bit more heavy cream and if it's too sticky (sticking to your hands a lot), add a little more flour.
Turn the dough out onto a lightly floured surface. Lightly flour your hands. Knead the dough just a couple of times then pat it into a 1 ½ inch tall circle. Aim for a circle between 6 and 8 inches. Use a sharp knife to slice the dough into 8 triangles (similar to slicing a pie). Place scones evenly spaced apart onto a baking sheet covered with parchment paper. Sprinkle tops of scones with granulated sugar.
Place scones at least 2 inches apart on prepared baking sheets. Brush tops and sides with milk. Sprinkle tops of scones generously with granulated or coarse sugar. Refrigerate scones 15 minutes.
Preheat oven to 400 F. Bake scones for 17-20 minutes or until golden brown around the edges and lightly browned on top.
Allow scones to cool. Drizzle with lemon icing, if desired.
Lemon Icing
In a medium sized bowl, sift the powdered sugar. Add the lemon zest and juice and use a whisk or spoon to combine.