For the cookies, position racks in the top and bottom thirds of the oven; preheat to 400°. In a small bowl, microwave the chocolate on medium in 30-second bursts, stirring occasionally, until melted. Transfer to a large bowl. Add 1/2 cup water and the remaining cookie ingredients, except the flour and chocolate chips. Using an electric mixer on low, beat until the ingredients are well blended, stopping occasionally to scrape down the sides of the bowl, about 2 minutes. Add the flour and chocolate chips and beat on low until blended, about 1 minute.
Using a 1 1/2-inch (1 tbsp.) cookie scoop, scoop the dough onto two nonstick or parchment-lined baking sheets, spacing about 2 inches apart. Bake until the cookies spring back when pressed with a finger, rotating the sheets and reversing from the top to bottom racks halfway through baking, 7 to 9 minutes. Transfer the cookies to a wire rack; let cool. Repeat with remaining dough on clean, cold baking sheets.
For the toppings, sift the confectioners' sugar and cocoa powder into a medium bowl. Whisk in the butter, 1 tbsp. milk and the vanilla, adding more milk by the teaspoon until a smooth, creamy frosting forms. Dip the tops of the cookies into the frosting; top with the crushed candy. Let stand until set, about 30 minutes.