Sift together flour, baking powder, salt and sugar. Using 2 forks or pastry blender, cut in butter to coat the pieces with flour until mixture looks like coarse crumbs. Make a well in center and pour in heavy cream. Fold everything together just to incorporate; do not overwork dough. Toss blueberries in a little flour then fold them into the batter, taking care not to mash or bruise them.
Gently press dough out on a lightly floured surface into a rectangle about 12x3x1-½ inches. Cut in half, then cut the 2 pieces in half again. Cut the squares in half on a diagonal.
Place triangles on ungreased cookie sheet and bake for 15 to 20 minutes until brown. Let cool a bit before applying glaze.
Preheat oven to 400 degrees F. To make glaze, mix lemon juice and confectioners’ sugar together in a microwave-safe bowl. Stir until sugar dissolves. Add zest and butter.
Microwave for 30 seconds on high. Whisk the glaze until smooth and drizzle over the tops of the scones. (Or make the glaze in a double boiler.) Let sit a minute before serving.