In a large bowl, whisk together flour, sugar, lemon zest, baking powder, and salt. Cut in the frozen butter until pea-sized crumbs form, then place the bowl in the freezer while you prep the wet ingredients.
In a measuring cup, whisk together heavy cream, egg, and vanilla until smooth.
Remove the flour mixture from the freezer. Pour in the wet ingredients, add blueberries, and gently fold until just combined.
Turn dough onto a floured surface, bring together into a ball, then press into a 7-inch disc about 1 inch thick. Cut into 8 wedges.
Stir together water and remaining tablespoon of cream, brush over tops, and sprinkle with coarse sugar. Chill for at least 15 minutes.
Bake at 400°F for 22–25 minutes until golden.
Cool for 5 minutes.
Whisk together glaze ingredients and drizzle over slightly warm scones.
