Preheat the oven to 400°F. Line a baking sheet with parchment paper.
In a large bowl, whisk together the flour, baking powder, baking soda, and salt. Set aside.
In a small bowl, lightly whisk the egg.Whisk in the sour cream. Set aside.
In another small bowl, place the sugar, zest, lilac flowers and lemon juice. Mix together well. Stir the sugar mixture into the flour mixture. Add frozen butter and, using your fingers or a pastry blender, blend until the mixture is pebble-like. Stir in the egg/sour cream mixture until the dough forms a ball (use your hands if it's easier).Divide the dough in half. You may need extra flower around because it will stick to your hands. It doesn't hurt to add a little in the mix or on your hands tohelp.
Place one dough portion on a lightly floured surface and press it into a 6-inch round. (It should be about ¾ to 1inch thick.) Cut the round into 6 wedges. Arrange the wedges 1 inch apart on the prepared baking sheet.Repeat with the second dough portion.
Bake until golden, 13 to 15 minutes.Cool on the baking sheet for 5 minutes, then transfer the scones to a wire rack set on a baking sheet.
Meanwhile, make the glaze: In a medium bowl, stir together the powdered sugar and zest. Stir in the melted butter, syrup, and lemon juice mixing until smooth.
Spoon the glaze over the scones.Serve the scones warm or at room temperature. Once glazed, the scones are best eaten the same day. Store unglazed leftovers in an airtight container at room temperature for up to 3 days.