Position a rack in the center of the oven and heat to 350°F. Line a 10-inch springform or Bundt pan with parchment paper. Sift confectioners' sugar, flour, cocoa and ground ginger in a bowl; set aside. Using a mixer fitted with the whisk attachment on medium speed, whip egg whites, vanilla, cream of tartar and salt until whites begin to form soft peaks, 1 to 2 minutes. Increase speed to high, add 6 tablespoons granulated sugar and whip until incorporated.
Add remaining 3/4 cup granulated sugar in 2 increments and whip until whites hold stiff peaks, about 2 minutes. Gently fold dry ingredients into egg mixture with a spatula.
Pour batter into pan.
Bake until cake springs back when touched, 35 to 40 minutes.
Remove from oven and cool completely. Loosen edges with a knife; transfer to a serving platter. Chocolate glaze: Bring half-and-half to a boil in a saucepan over medium-high heat. Reduce heat to a low simmer and add chocolate and confectioners' sugar; whisk until chocolate melts and mixture is smooth.
Pour glaze over top of cake, allowing it to drip down sides. Top with candied ginger. Store at room temperature in a cake saver for up to 3 days.
