Chocolate-Covered Digestive Biscuits (McVities)

Name: Chocolate-Covered Digestive Biscuits (McVities)
Total time: 90 min
Yield: 16
Ingredients: 4 1/2 ounces all-purpose flour (about 1 cup, spooned; 125g); 2 ounces whole wheat flour (about 1/3 cup; 55g), plus more for dusting; 2 1/4 ounces sugar (about 1/3 cup; 60g); 1/4 teaspoon baking powder; 1/4 teaspoon baking soda; 1/8 teaspoon (1/2g) Diamond Crystal kosher salt; for table salt, use about half as much by volume or use the same weight; 4 ounces cold unsalted butter (about 8 tablespoons; 113g), cut into 1/4-inch cubes; 2 ounces cultured lowfat buttermilk (about 1/4 cup; 55g); 9 ounces roughly chopped dark or milk chocolate (about 1 1/2 cups; 285g) (see note)