Preheat oven to 375 F. Line a baking sheet with parchment paper. Combine the dry ingredients in a bowl. Cut in butter with a blender or fork until bean sized. Stir in cheddar cheese and chives, add buttermilk and 2 Tbsp water. Knead gently until blended. Turn dough out onto a lightly floured board and pat into an 8 inch square. Cut into 2 inch squares, then cut diagonally into triangles. Arrange on a baking sheet spacing approx. 1 inch apart. Brush tops with egg-water mix and bake until golden--about 25 minutes.