Preheat the Oven: Heat the oven to 220°C/200°C fan/430°F. Line a baking tray and place it in the oven so the tray preheats.
Combine the Dry Ingredients: Add the self-raising flour, sea salt, optional baking powder, and caster sugar to a large mixing bowl. Stir them together until evenly distributed.
Rub in the Butter: Add the cold, cubed butter and rub it into the flour mixture with your fingertips until the mixture resembles fine breadcrumbs. Alternatively, place the flour, salt, baking powder, sugar, and butter in a food processor and pulse until breadcrumb-like. Add the Lemon: Mix the lemon juice and lemon zest into the dry mixture until incorporated.
Add the Milk: Gradually pour in the 185 ml warm full-fat milk, mixing as you go with a spatula. Add the milk slowly because you may not need every drop; stop once the mixture forms a workable dough.
Fold in the Blueberries: Gently fold the 150 g fresh blueberries through the dough, distributing them as evenly as possible without overworking the mixture.
Shape the Dough: Lightly dust the work surface with flour and turn the dough out onto it. Fold the dough over itself a few times until it becomes smoother, taking care not to knead or work it excessively.
Flatten the Dough: Gently flatten the dough until it is approximately 5 cm thick.
Cut the Scones: Dip a 5 cm round cutter into the extra flour, then cut out the scones. Transfer each one to the preheated baking tray.
Reuse the Dough: Gather and gently flatten the remaining dough, then continue cutting scones until all the dough has been used. Handle it as little as possible to avoid overworking it.
Glaze the Tops: Brush the tops of the scones with the beaten egg, giving them an even glaze.
Bake: Place the tray in the oven and bake for 10 minutes, until the scones are baked through and lightly golden.
Cool and Serve: Remove the scones from the oven and allow them to cool slightly before serving.
