Preheat oven to 375 degrees F. Spray a baking sheet with cooking spray or line with a piece of parchment paper.
Combine the first four ingredients in a medium bowl, stirring with a wire whisk. Set aside.
Combine flour, baking powder, and salt in a large bowl, whisking to combine. Cut in the chilled butter with a pastry blender (or 2 knives) until the mixture resembles coarse meal.
Gently fold in chocolate chips.
Add buttermilk mixture to dry mixture, stirring just until moist.
Place dough onto a floured surface and knead lightly four times with floured hands. Form dough into a 9-inch circle onto the baking sheet, about 3/4-inch thick.
Using a knife, cut dough into 12 wedges all the way through.
Brush egg white over dough and sprinkle evenly with sugar.
Bake until golden, about 18 - 20 minutes. Serve warm.