Preheat oven to 400 degrees F. Lightly grease or line two baking sheets with parchment.
In a large bowl, mix together flour, sugar, baking powder, and salt. Cut in the cold butter using a dough blender, two forks, or your fingers. The texture should become coarse with no pieces larger than a pea.
In a measuring cup, add egg and egg yolk. Pour in buttermilk until mixture reaches 1 cup. Add the chives and whisk together until eggs are incorporated. Pour into the flour mixture and gently combine until dough forms.
On a lightly floured surface, gently pat the dough until it is 1/2 inch thick. Flour a 3 inch biscuit cutter and cut out biscuits. Place on prepared baking sheets. Bake in preheated oven until golden, 12-15 minutes.