Preheat oven to 400 degrees F. Line baking sheet with parchment paper.
In a large bowl, whisk together flour, salt, sugar, baking powder, lemon thyme, and lemon zest.
Add chilled butter cubes to dry mixture. Cut in butter using a pastry blender, a fork, or your fingers until mixture resembles coarse sand.
Reserve 1 Tbsp of heavy cream. Pour remaining cream into mixture and stir until combined. Turn dough onto a lightly floured surface and gently pat/roll out to a little over 1/2 inch thickness.
Cut biscuits using a 2 1/2 inch round cutter dipped in flour. Arrange biscuits on prepared baking sheet. Gather remaining dough and roll out again to punch out more rounds.
Brush reserved 1 Tbsp of heavy cream over the tops of biscuits. Sprinkle with turbinado sugar. Bake for 15-18 minutes until biscuits are golden.