Preheat the oven to 400 degrees F.
Sift together the dry ingredients; the flour, baking powder, salt, and sugar. Using 2 forks or a pastry blender, cut in the butter to coat the pieces with the flour. The mixture should look like coarse crumbs. Make a well in the center and pour in the heavy cream. Fold everything together just to incorporate; do not overwork the dough. Fold the blueberries into the batter. Take care not to mash or bruise the blueberries because their strong color will bleed into the dough.
Press the dough out on a lightly floured surface into a rectangle about 12 by 3 by 1 1/4 inches. Cut the rectangle in 1/2 then cut the pieces in 1/2 again, giving you 4 (3-inch) squares. Cut the squares in 1/2 on a diagonal to give you the classic triangle shape. Place the scones on an ungreased cookie sheet and brush the tops with a little heavy cream. Bake for 15 to 20 minutes until beautiful and brown. Let the scones cool a bit before you apply the glaze.
Technically you should make this simple lemon glaze in a double boiler (i.e. over a pot of simmering water with a heatproof bowl set on top) but it's even simpler to zap it in the microwave. Mix the lemon juice and confectioners' sugar together in a microwave-safe bowl. Stir until the sugar dissolves. Add the lemon zest and butter. Nuke it for 30 seconds on high. Whisk the glaze to smooth out any lumps, then drizzle the glaze over the top of the scones. Let it set a minute before serving.