Place a rack in the center of the oven and heat to 200º C. Line a baking sheet with parchment paper or a nonstick baking mat and set aside.
In a large bowl, whisk together the flour, sugar, baking powder, baking soda, garlic, salt and pepper. Add the butter and work it with the tips of your fingers until the mixture is coarse and unevenly crumbly.
In a small bowl, whisk together the egg, water and sour cream. Add the wet ingredients to the flour mixture. Using a rubber spatula, mix until a moist dough forms. Stir in the cheddar and chives, then transfer the dough onto a well-floured work surface.
Knead the dough until it holds together, then pat it into a 1-inch thick round. Cut into 2-inch rounds using a biscuit cutter. Continue to reshape the dough scraps as needed until all the dough is used.
Place the dough rounds on the prepared baking sheet and brush with the beaten egg. Sprinkle each with additional salt and pepper, then bake for 16-20 minutes.
To make ahead and freeze, simply line a baking sheet with parchment or wax paper and place the unbaked scones on it. Freeze until the scones are firm, then transfer to an airtight container. Bake directly from the freezer, adding a couple minutes to the original baking time.