Combine flour, sugar, sea salt, and baking powder in a large bowl.
Using a microplane or cheese grater, shred your cold butter onto the flour mixture. Once done, place bowl in freezer for 10 minutes.
While chilling, blend buttermilk, 1/4 sour cream, and 1/3 cup Maine blueberries in a blender or food processor. Don't over-mix or the mixture will split.
Remove flour and butter bowl from freezer and work butter pieces into flour with a fork or your hands. The mixture should resemble coarse sad.
In 3 batches, add your blueberry buttermilk mixture to the biscuit dough and gently work together until no liquid is left. Do not over-mix.
Add the last of your liquid and bring dough together into a shaggy dough. Transfer mixture to a floured work surface.
Bring the dough together into a large rectangle. Using a bench scraper, cut half of the dough and place it on top of the other half, pressing gently. The dough will be crumbly and hard to work with at first.
Repeat this step, but this time add 1 cup of blueberries on the dough first and place the other half on top, securing the blueberries in the middle.
Continue cutting the dough and placing one layer on the other, 1-2 more times, until dough is cohesive and no shaggy bits remain.
Form dough into a thick 9" x 9" square, about 1 1/2 to 2" tall. Cut square into 9 equal biscuits and place on a parchment-lined baking sheet.
Preheat oven to 375°F and place biscuits in the freezer to chill for 10 minutes before baking. Then, place sheet of biscuits in the oven to bake for 25 - 35 minutes, until golden brown and risen.
Let biscuits chill at room temperature for 20-30 minutes. In the meantime, add powdered sugar to a large bowl.
In a food processor or blender, combine 1/3 cup of blueberries with 2 tbsp of lemon juice. Blend until you have a loose purple liquid.
Strain blueberry liquid into the powdered sugar, starting with about 1/4 cup. Add more strained juice, 1 tsp at a time, until the icing is thick but pourable.
Dip the tops of each biscuit into the blueberry icing and flip back over to rest on a wire rack or cool baking sheet.
When ready to eat, heat biscuits gently or split them open and toast, lathering with butter, cream, or jam.