Preheat the oven to 400 degrees F. Line a sheet pan with parchment or silicone mat.
In the bowl of an electric mixer or food processor, combine the flour, sugar, baking powder and salt. Add the butter and, with the mixer on low speed (or the food processor on “pulse”), mix the butter into the flour until the butter is the size of peas. If you don’t have a stand mixer or a food processor, you can freeze the butter and grate it into the dry ingredients, or you can cut the butter into the flour by hand with a pastry cutter or with two knives.
In a large measuring cup or small bowl, whisk together ⅔ cup of cream and 1 of the eggs. Gradually add the wet ingredients to the dry ingredients and stir just until blended. Do not over-mix. The dough should be sticky and damp. If it's too dry, add a little bit more cream (up to 1 cup may be necessary). If it's too wet, sprinkle in a little bit of extra flour. Gently fold in the blueberries.
Dump the dough onto a very well-floured surface and knead it lightly and quickly just a few times. It helps to put flour on your hands to prevent sticking. Pat the dough into a circle that’s 1-inch thick. Using a pizza cutter or knife that is sprayed with cooking spray before each slice, cut the circle into 6-8 wedges, depending on how large you like the scones.
Transfer the dough to the prepared baking sheet, leaving 2 inches between each scone.
Beat the remaining egg with 2 tablespoons of water or cream to make an egg wash. Brush the tops of the scones with the egg wash, sprinkle with sugar, and bake for 20-25 minutes (or until the tops are lightly browned and the insides are fully baked). Serve warm or at room temperature.