Chocolate Fudge Cookies Store

Ingredients
2 1/4 cups (255g) confectioners' sugar
1/4 teaspoon salt
1 teaspoon espresso powder, optional but good
1 cup (85g) unsweetened cocoa, Dutch-process or natural
3 large (106g) egg whites
2 teaspoons vanilla extract
2 cups (227g to 340g) chocolate chips, chopped nuts, and/or chopped dried fruit, optional