Combine dry ingredients. Whisk together flour, sugar, baking powder and salt in a large bowl.
Add butter. Cut in butter with a pastry blender or rub in with your fingers, until the mixture has the texture of coarse meal.
Add mix-ins. Fold in blueberries and lemon zest.
Add wet ingredients. Whisk together heavy cream, egg, and vanilla. Make a well in the dry ingredients, and pour in the heavy cream mixture. Stir lightly with a wooden spoon or spatula until dough comes together. Dough will be sticky and shaggy looking.
Knead dough. Turn out dough onto a lightly floured surface, and gently knead dough together a few times. I press down on the dough into about 1/2" thickness, then fold in half. I repeat this about 3-4 times. Do not overwork the dough, you just want to incorporate the flour and bring it together.
Shape scones. Pat dough into an 8" circle. Cut into 8 wedges. Transfer to baking sheet and refrigerate for 15 minutes.
Prep oven and pan. Preheat oven to 400°F. Line a baking sheet with parchment.
Bake the scones. Bake until golden brown and cooked through, about 20-22 minutes. Transfer scones to wire rack to cool.
Make lemon icing. Combine icing ingredients in a bowl and whisk to combine. Adjust consistency if needed. Drizzle cooled scones with icing.