Dough 2 ¼ teaspoons active dry or instant yeast ¾ cup warm water ½ teaspoon + 2 tablespoons sugar 4 cups unbleached flour plus more for dusting 1 teaspoon salt 2 large eggs 1/3 cup vegetable oil 2 tablespoons additional sweetener (sugar, honey or molasses)
Filling ¾ cup chopped dark chocolate 8 tablespoons unsalted butter, room temperature 1/3 cup unsweetened cocoa, Dutch-process or natural ½ cup confectioners’ sugar
Combine the yeast, warm water, and 1/2 teaspoon of sugar and give it a little stir. Let it sit for about 5 minutes, until it becomes foamy on top.
In a large bowl mix together the flour, salt, and remaining 2 tablespoons sugar. In a medium bowl, whisk together the eggs, oil, and additional sweetener.
When the yeast is foamy, add it to the dry mixture immediately followed by the egg mixture and stir to combine. Knead until you have a smooth and slightly sticky dough, 7 to 10 minutes, adding more flour as necessary.
Transfer the dough to an oiled bowl, cover it with plastic wrap, and let it sit at room temperature until doubled in size, 1 1/2 to 2 hours.
While the dough is rising, make the filling: Place the chocolate, butter, and cocoa powder into a medium heat-proof bowl and microwave in 30-second increments until the chocolate is completely melted, stirring after each (it will take around 2 minutes).
Add the confectioners’ sugar, mixing until thoroughly incorporated. Set aside to thicken, about 30 minutes; the mixture should be the consistency of soft ganache.
To assemble the king cake: Divide the dough in half. Working with one piece at a time, roll the dough on a lightly floured surface into a 15” x 11” rectangle.
Spread half the chocolate mixture over the dough, leaving a 1/2” border around the edges.
Starting from the long side closest to you, roll the dough into a log. Rest the log on its seam.
Gently cut the roll in half lengthwise, starting at the top.
With the cut sides facing up, gently alternate crossing the pieces over each other to create a two-strand braid.
Repeat with the second piece of dough and remaining chocolate filling.
Line a large baking sheet with parchment paper. Gently transfer the two braids to the prepared pan and shape them into one large circle, joining together the ends for continuity.
Cover with lightly greased plastic wrap and allow to rise in a warm place for 1 1/2 hours; the king cake won’t double in size, but will rise slightly. Towards the end of the rising time, preheat the oven to 350°F
Remove the plastic wrap. Bake the king cake for 25 to 30 minutes, until a skewer inserted into the center of the dough comes out clean and all of the exposed chocolate swirls are firm to the touch.
While the king cake is baking, make the glaze. Combine the water and sugar in a small saucepan and bring to a boil over medium heat. When the sugar is fully dissolved, remove from the heat and set aside.
As soon as the king cake comes out of the oven, brush all of the glaze over the king cake; it will seem like a lot, but just keep brushing.
Slide the king cake from the baking pan to a cooling rack. Allow to cool completely before decorating.
While the king cake is cooling, make the icing. In a small bowl, mix powdered sugar, milk and vanilla until smooth (add additional milk if mixture is too thick or powdered sugar if too thin).
Spoon icing over top of the cake. Immediately sprinkle on colored sugar, alternating between the three colors.
Store any leftovers, well wrapped in plastic, at room temperature for up to 3 days; freeze for up to a month.