Preheat and prepare pan. Preheat your oven to 450oF. Line a cookie sheet with parchment paper or silicone baking mat, or you can bake these in a cast iron, or lightly greased round cake pan.
Combine dry ingredients. In a mixing bowl, whisk together flour, baking powder, sugar, and salt.
Cut in butter. Using your fingertips, two knives, or a pastry blender, cut the butter into the dry ingredients until the butter is pea-sized. Stir in lemon zest and blueberries. Pour in cold buttermilk, and vanilla and stir to combine.
Knead the dough. The dough will be pretty wet and sticky at this point. Just pour the dough onto a lightly floured surface or one of these pastry mats. And bring the dough together gently. You want to handle the dough as little as possible. Overhandling the dough will develop the gluten in your biscuits, which will in turn make the texture of your biscuits very tough. So handle as little as possible. But you will knead the dough together about 3 times which will help to create the layers.
Cut out the biscuits. After you have kneaded the dough together a few times then pat the dough into a 3/4-inch to 1-inch thick circle. Cut out the biscuits using a 2 ½ to 3 inch biscuit cutter. Press the scraps together and cut out remaining biscuits. Try to handle the dough as little as possible.
Bake the biscuits. Arrange biscuits onto either parchment lined cookie sheet, in a round baking dish or in a cast iron. Bake for 15 minutes until golden brown.
Make the glaze. In a small bowl, stir together the confectioner sugar, lemon juice and vanilla. Spread glaze over warm biscuits before serving.