In a large bowl, whisk together the flour, sugar, lemon zest, baking powder, and salt. Using the large holes of a box grater, shred the frozen butter. Add the butter to the flour mixture and use a pastry cutter, two forks, or your fingers to blend until the mixture comes together in pea-sized crumbs. Place the bowl in the freezer before you continue.

In a small bowl or liquid measuring cup, whisk together 1/2 cup (120g/ml) of the heavy cream, the egg, and vanilla extract. Remove the flour mixture from the freezer. Drizzle the cream mixture over the flour mixture and add the blueberries. Gently mix together with a spatula or wooden spoon until everything appears moistened and the ingredients are just combined.

Lightly flour a work surface. Pour the crumbly mixture onto the surface and, with floured hands, work the dough into a ball as best you can. The dough should be sticky and shaggy. If it’s too sticky, sprinkle a little more flour on top. Press the dough into an 8-inch disc, about 1 inch thick. Use a sharp knife or a bench scraper to cut the disc into 8 wedges.

In a small bowl, mix the remaining 1 Tablespoon cream with the water, then brush it on the scones. For extra sweetness and a little crunch, sprinkle the tops with coarse sugar. (You can do this before or after refrigerating in the next step.) Place the scones on a plate or a parchment paper-lined baking sheet and refrigerate for at least 15 minutes or up to 24 hours. (If refrigerating for more than an hour, lightly cover the scones.)

Preheat the oven to 400°F (204°C). Line a large baking sheet with parchment paper or a silicone baking mat. Arrange the chilled scones 2–3 inches apart on the prepared baking sheet.

Bake for 22–25 minutes or until lightly browned on top and golden around the edges. Cool the scones on the baking sheet for 5 minutes before icing.

In a small bowl or liquid measuring cup, whisk together the confectioners’ sugar and lemon juice. Drizzle the icing over the scones.

Store leftover scones covered tightly at room temperature for up to 2 days or in the refrigerator for up to 5 days.