Preheat oven to 400 degrees.
Line a large baking sheet with parchment paper. Set aside.
Place the flour, sugar, baking powder, salt and lemon zest in the bowl of a stand mixer. Whisk together.
Add the butter and mix on low-speed until mixture resembles pea-sized crumbs.
Slowly add the heavy cream and egg until the dough forms a thick clump.
Turn the dough out onto a lightly floured surface.
Roll the dough out into a large rectangle 1/2 inch thick.
Cut out 18 rounds using a 2 inch biscuit cutter.
Place on prepared tray. Brush with some extra heavy cream.
Bake for 12 minutes or until lightly golden brown.
Combine all ingredients in a small bowl and whisk together.
Drizzle over warm scones.