It's fine to freeze the scones ahead as directed below; the baking time may be slightly longer. These are amazing scones! Perfect for tea or dessert or even breakfast! YUM! Prep time includes 30 minute freezing time for butter.
Preheat the oven to 375°. Line 2 baking sheets with parchment, or grease them with butter.
Chop the butter into 1/4-inch pieces. (It is important to make the pieces no larger than 1/4 inch because they are difficult to make any smaller once frozen.) Spread on a plate and place in the freezer until hard, about 30 minutes or overnight.
Combine the flour, sugar, baking powder, salt and baking soda in a large bowl.
Add the butter, and chop with two butter knives or a pastry blender until it is well blended and some of the butter is crumbly. Mix in the pecans.
Gradually add the buttermilk, 1/3 cup at a time, and mix gently until all ingredients are incorporated but not completely blended. You might not use up all of the liquid. The end result should be a shaggy mass.
Sprinkle the blueberries on top of the dough and only mix enough to evenly distribute the berries.
Gently form the dough into 1/3-cup balls and place them 1 inch apart on the prepared baking sheets. (You may freeze the balls at this point and bake them later. Once frozen, place scones in freezer storage bags.).