Preheat the oven to 200C/400F/Gas 6. Line a baking tray with parchment paper or a silicone mat, and set aside.
In a large bowl, whisk together the flour, sugar, baking powder, salt, and zest. Add the butter and, using a pastry cutter, fork, or your fingertips, work it into the mixture until it resembles coarse breadcrumbs. You may also use a food processor.
In a separate bowl, whisk together the egg, cream, and lemon extract until combined. Pour into the flour mixture and gently fold in until a soft dough is formed. Do not overmix.
Turn the dough out onto a lightly floured surface, and shape into an 8-inch round disc. Cut into 8 wedges, and transfer them to the prepared baking tray.
Lightly brush each scone with heavy cream, then bake for 20 - 25 minutes or until lightly golden and cooked through. Allow to cool on the baking tray for 5 - 10 minutes before transferring them to a wire rack to cool slightly whilst preparing the glaze.
For the Glaze
Whisk together the icing sugar, extract, and milk until smooth and slightly runny. Add more milk if the glaze is too thick, or more icing sugar if too runny. Drizzle over warm or room temperature scones, and enjoy!
Notes
Scones are best warm on the day they are made, but leftovers can be kept in an airtight container at room temperature or in the fridge for up to 2 days. They also freeze well for up to 3 months. Thaw overnight in the fridge before serving.