Preheat oven to 325°
In a mixing bowl, place flour, sugar, baking powder, salt and the zest, and mix together using a whisk. Make a well in the center. Set aside.
Chop up your cold butter into 1/4 inch pieces. Place chopped butter into the dry ingredients, and cut the butter into the dry ingredients. You can use two forks, a pastry cutter or your hands. I use my hands and pinch the butter between my fingers. Cut in the butter until the pieces are pea-sized.
In a separate bowl, whisk together the eggs, vanilla and 1/2 cup of heavy cream. Pour into the well that you made in the first bowl.
Use your hands to incorperate your liquids into your dry/butter mixture. Once it starts to come together, and you have just a little of the dry ingredients in the bottom of your bowl, add in your frozen blueberries. Mix with your hands until the berries are incorperated, and your dough has come together.
Turn out dough onto floured surface, and roll into a long log. Use a knife or a bench scraper to cut your dough into the desired size. Or you can roll your dough into a 3/4 inch thick disk and cut out triangles.
Place on a sheet pan with parchment. Use a pastry brush, and brush your scones with your leftover heavy cream. Sprinkle with sugar. Bake until light brown on the bottom and when they spring back when you touch them in the middle. Once finished, slather in butter or your favorite jam. Baking time: 15-17 minutes for small scones. 28-30 minutes for large scones.
