Preheat the oven to 400°F. Get out a large baking sheet.
Combine the flour, sugar, baking powder, salt, and lemon zest in a large bowl and whisk to mix. Add the butter and, using a pastry blender or your fingers, cut it into the dry mixture to make very small pieces. Make a well.
Combine the yolk, cream, and vanilla in a small bowl and stir to blend. Pour into the well and stir until the dough pulls together. Set aside to rest for 3 to 4 minutes.
Lightly flour a work surface.
Scrape the dough onto the work surface and dust your hands and the dough with flour. Knead the dough gently 4 or 5 times. It will be soft but manageable. Shape the dough into a ball, then flatten it into a disk about 3⁄4-inch thick and 7 to 7-1⁄2 inches in diameter. Cut the disk into eight equal pie wedges. Place the wedges on the baking sheet, evenly spaced. Lightly brush the tops with cream.
Bake for 15 to 17 minutes, or until golden, and transfer to a cooling rack.
Sift the confectioners’ sugar into a bowl. Add the corn syrup and 1 tablespoon of milk and stir with a wooden spoon, until smooth. Add the lemon extract and stir to blend. Add additional milk, ½ teaspoon at a time, and whisk until the glaze is runny but still thick.
When the scones are barely warm, place them on a sheet of wax paper or plastic wrap and drizzle them generously with the glaze. Garnish with lemon zest.