Step 1Heat the oven to 350 degrees. In the bowl of a stand mixer using the beater attachment, or in a large bowl using a hand mixer, beat the butter and 1 cup sugar until light and fluffy, 3 to 5 minutes. Add the eggs, one at a time, until thoroughly incorporated. Beat in the orange zest and one-third cup juice.
Step 2In a medium bowl, sift together the flour and baking powder. With the mixer running, slowly add the flour mixture until combined to form the cake batter. Fold in the chopped chocolate.
Step 3Place the batter into a greased and floured 9-inch bundt pan, smoothing the top of the batter. (The batter will come slightly less than halfway up the sides of the pan.)
Step 4Bake the cake until puffed and lightly browned on top and a toothpick or cake tester inserted comes out clean, 45 to 55 minutes. Remove from the oven and cool in the pan on a cooling rack, then remove from the mold. The finished cake will be about 3 inches tall in the center.
Step 5While the cake is cooling, make the icing: In a medium bowl, sift the powdered sugar. Add the remaining 2 tablespoons orange juice and whisk to form the icing.
Step 6Drizzle the icing over the cooled cake, then garnish with the candied orange.