Chill your tools. Pop a mixing bowl, the butter, and even the flour in the fridge for 10 minutes if your kitchen is warm. The colder the fat, the better the rise. Heat the oven to 400°F (200°C) and line a baking sheet with parchment.
Whisk the dry ingredients. In your chilled bowl, whisk flour, sugar, baking powder, and salt. Add lemon zest if you’re using it. It gives a sunny lift, not overpowering.
Cut in the butter. Add the cold butter cubes and work them into the flour with a pastry cutter or your fingertips. Aim for pea-sized bits with some larger, flattish pieces. Think “shaggy and crumbly,” not smooth. Those buttery pockets make flaky layers.
Mix the wet ingredients. In a small bowl, whisk the cream, egg, and vanilla until combined.
Bring it together. Make a well in the flour mixture and pour in the cream mixture. Gently fold with a spatula until most of the flour is moistened. It will look a bit rough. That’s okay.
Add the blueberries. If using fresh, fold them in gently. If using frozen, toss them with a teaspoon of flour first, then fold in, working quickly so they don’t stain the dough too much. Some purple swirls are part of the charm.
Shape the dough. Turn the dough onto a lightly floured surface. Pat it into a 7 to 8 inch disc, about 1 inch thick. If it’s crumbly, press it together with confident hands, but don’t knead. Overworking makes tough scones.
Cut and chill. Slice the disc into 8 wedges. Transfer to the prepared baking sheet, leaving space between each. Brush tops with a little cream and sprinkle with coarse sugar if you like a delicate crunch. Slide the tray into the freezer for 10 to 15 minutes. This quick chill helps the scones keep their shape and rise tall.
Bake. Bake at 400°F (200°C) for 18 to 22 minutes, until the tops are golden and the edges look set. You want a firm top but still tender inside. If your oven has hot spots, rotate the pan once.
Cool slightly. Let the scones rest on the tray for 5 minutes, then move to a rack. If glazing, whisk the powdered sugar with lemon juice to a drizzle and spoon it over warm scones. Tiny glossy ribbons. Very satisfying.
Serve. Best slightly warm, with butter, jam, or just as they are. Save one for later if you can… good luck with that.