Heat oven to 425°F. Line a baking sheet with parchment.
Whisk flour, sugar, baking powder, baking soda, and salt in a large bowl.
Cut in the cold butter with a pastry cutter until the mix looks like coarse crumbs with pea-size bits.
Stir in lemon zest and vanilla. Add buttermilk and mix just until a shaggy dough forms.
Gently fold in blueberries. If dry spots remain, sprinkle in 1–2 teaspoons buttermilk.
Turn dough onto a floured surface. Pat into a rectangle, fold in thirds, and repeat once for flaky layers.
Press to about 1 inch thick. Cut 8 rounds with a floured 2.5-inch cutter, gathering scraps as needed.
Arrange biscuits on the sheet so they just touch. Brush tops with cream and sprinkle with coarse sugar.
Bake until risen and golden, 14–17 minutes. Cool 10 minutes on a rack.
Whisk powdered sugar, lemon juice, milk, and a pinch of salt until smooth. Adjust thickness to drizzle.
Drizzle glaze over warm biscuits. Let set a few minutes before serving.