Procedure:

1) Freeze the butter, wrapped, on a dinner plate overnight. Before unwrapping, mark the 5 Tablespoon line with a notch. Fold the butter wrapping paper around the short end of the stick. Hold the paper-wrapped end of the stick in one hand and place the other end on a plastic or wooden cutting board. Using a very sharp knife, shave off peels of butter. If the butter shatters or breaks while shaving, it is too cold. Let it rest 5 minutes before proceeding. As you work, stop occasionally to toss the butter shavings onto the dinner plate. When all the required butter has been shaved, place the plate and shavings into the freezer.

2) Place an oven rack in the center position and heat oven to 425 F. Place a sheet of parchment on the sheet pan.  Measure blueberries into a small bowl and hold in the refrigerator. In a medium bowl, whisk milk and sour cream together, and place into freezer while mixing dry ingredients. In a separate medium bowl, whisk together the flour blend, the xanthan gum, the sugar, the baking powder, the salt, the baking soda and the lemon zest, stirring until thoroughly blended. Add the chilled butter shavings and toss with your fingers until they are evenly distributed. Add the chilled milk and sour cream and fold in gently with a spatula until flour is just barely wet.

3) Turn the dough out onto a dusted work surface. Dust your hands and gently shape the dough into a rough square. Use a dusted rolling pin to roll dough into an 8 inch X 8 inch square. Roll gently and occasionally use a plastic bench knife or metal spatula to tap the edges into straight lines. Run the spatula under the dough square, then fold the bottom third up onto the middle third, and the top third down onto the other two thirds. The resulting rectangle will be about 3 inches X 8 inches. Fold half the long dimension over the other half of the long dimension to create a 3-inch X 4-inch rectangle and place this into the freezer for 5 - 8 minutes.

4) Remove dough from freezer and place onto well-dusted work surface.  Roll out to an 8-inch X 8-inch square. Run the spatula under the dough to loosen it. Scatter the blueberries evenly across the top of the dough square. Loosen dough one more time, then roll into a  "log" that is 8 inches long. Dough may break in places; pinch edges together to seal the seam. Gently roll this log into a rectangle that is 4 inches tall X 10 inches long. Cut the rectangle into thirds, then cut diagonals across the resulting small rectangles, creating 6 triangles.

5) Place onto parchment on the baking sheet, brush with melted butter, and sprinkle with sugar. Bake 19 - 25 minutes, rotating the tray mid-time. Remove to a cooling rack and have some lunch. For dessert, eat one or two or three while they are still warm and remove the rest from the pan to finish cooling on the rack. When spouse appears and claims you've eaten all the best ones, produce vanilla ice cream and make a peace offering of scones a lá mode. Live happily ever after.