Preheat oven to 425F. Line a baking tray with parchment or a silicone baking mat.
In a large mixing bowl combine the flour, sugar. baking powder and salt.
Add the chilled butter to the bowl and cut the butter into the mixture using a pastry cutter or forks until the texture is like a coarse meal. This can also be done in a food processor with a few quick pulses,
In a small bowl whisk the heavy cream, egg, lemon juice and lemon zest. Add to the dry ingredients and combine using a wooden spoon. Do not over mix. Just bring it together as a slack dough.
Turn the dough out onto a lightly floured work surface and knead 3-4 times. Shape the dough into an 8" round whch should be about 1" thick. With a floured knife, cut into 8 wedges.
Transfer the wedges to the baking tray leaving room for them to rise. Brush with a little heavy cream on the tops only. Sprinkle with the turbinado sugar.
Bake for 12-15 minutes until lightly golden in color. Remove to a rack to cool fully before glazing.
Whisk together the icing sugar, lemon juice and zest adding the lemon juice a little at a time until the glaze is a thick but pourable consistency.
If not eaten within a couple of days freeze them in ziplock freezer bags. They will keep for up to 3 months.