Make the sugared cranberries: Put the cranberries in a medium bowl. Bring 1/2 cup sugar and the water to a simmer in a small saucepan over medium-high heat; cook, stirring, until the sugar dissolves, about 2 minutes. Pour over the cranberries and set aside 1 hour. Drain the cranberries, then toss with the remaining 1/4 cup sugar. Spread the cranberries and sugar on a baking sheet and set aside to dry, rolling occasionally in the sugar to coat, 2 to 3 hours.
Meanwhile, make the cupcakes: Preheat the oven to 350 degrees F. Line a 12-cup muffin pan with liners. Whisk the flour, cocoa powder, allspice, cloves and salt in a medium bowl. Whisk the molasses, sugar, vegetable oil and vanilla in a large bowl. Dissolve the baking soda in the boiling water in a liquid measuring cup, then whisk into the molasses mixture. Whisk in the flour mixture, then the egg, until combined.
Divide the batter among the prepared muffin cups, filling each about two-thirds of the way. Bake until the tops of the cupcakes spring back when gently pressed, about 22 minutes. Let cool 5 minutes in the pan, then transfer to a rack to cool completely.
Make the frosting: Beat the egg whites in a stand mixer fitted with the whisk attachment on medium-high speed until soft peaks form. Put 1/4 cup sugar on a large plate; set aside. Combine the remaining 1 cup sugar, the water and rosemary sprigs in a small saucepan over medium heat; cook, stirring, until the sugar dissolves. Increase the heat to medium high and bring to a boil. Cook until the syrup registers 235 degrees F on a candy thermometer, about 5 minutes; remove from the heat. Working quickly, remove the rosemary with tongs and transfer to the plate with the sugar; toss to coat, then set aside. Turn the mixer on high and slowly drizzle the hot syrup into the bowl with the egg whites, aiming the syrup between the side of the bowl and the beater. Continue beating until both the bowl and the mixture are cool to the touch, 12 to 15 minutes. Switch to the paddle attachment and beat in the butter on medium speed, 1 piece at a time, until the frosting is smooth and thick.
Transfer the frosting to a piping bag fitted with a large round tip; pipe onto the cupcakes. Top each with a few candied rosemary needles and 2 sugared cranberries.