Preheat oven to 425 F (220 C) and prepare a large baking tray with parchment paper.
In a large mixing bowl, hand whisk together the flour, salt, sugar, baking powder, and thyme.
Add in the cold butter cubes and work them into the flour using a pastry cutter or your fingertips until it resembles cornmeal with small pea sized chunks of butter remaining.
Add the cheddar cheese, and chives to the flour mixture and stir to evenly distribute with a wooden spoon or silicone spatula.
Stir together the heavy cream and egg in a cup using a fork or small whisk and pour into the dry mixture.
Stir with a wooden spoon until a shaggy dough is formed.
Use your hands to gently shape the dough into a fat disc. If the dough is to crumbly, add another tablespoon of cream to the mixture and pat together. Careful not to over work the dough.
Place the dough onto a lightly floured surface and gently roll it out to 1/2 inch thickness.
Use a 3-inch biscuit cutter to cut eight scones. (you may only be able to cut 6 at first, just take excess and reform, roll, then cut the last two.) Or, shape dough into a circle and slice like a pizza into eight slices.
Place scones on parchment paper lined baking tray about 2 inches apart.
Brush top of scones with heavy cream and sprinkle with extra cheese.
Chill the scones in the fridge for about 10 minutes before baking.
Place baking tray on the middle oven rack and bake for 18-20 minutes or until lightly golden brown. Serve warm.