For Cookies• 1 cup granulated sugar (200g)• ⅓ cup unsalted butter 5 ⅓ Tablespoons of butter (75g)• 1 large egg lightly beaten• 1 teaspoon vanilla extract• ¾ cup sour cream (170g)• 2 cups all-purpose flour (250g)• ½ cup dark cocoa powder see note (50g)• 1 teaspoon baking soda• ¼ teaspoon baking powder• ½ teaspoon salt• ½ cup very hot or boiling water (118ml)
Transfer to preheated oven and bake for 5 minutes, then allow cookies to cool for 5-10 minutes on baking sheet before carefully removing to a cooling rack.
Place white chocolate in a microwave-safe dish and heat in the microwave in 15-20 second increments, stirring well in between, until completely melted.