For the cake: Preheat the oven to 350°F.

Place the chocolate in a large bowl. In a medium saucepan, whisk together 1 ½ cups of water, the granulated sugar, brown sugar, and butter; bring the mixture to a simmer over medium heat, stirring occasionally, until the sugar is dissolved and the butter is melted. Whisk in the cocoa powder. Pour the hot mixture over the chopped chocolate, and let stand for 2 minutes. Stir until the chocolate is melted and the mixture is combined. Whisk in the sour cream, eggs, egg yolk, and vanilla. (The mixture will not be smooth.)

In a medium bowl, whisk together the flour, baking soda, and salt. Slowly add the flour mixture to the chocolate mixture, whisking just until combined.

Spray a 10- or 12-cup Bundt pan with baking spray with flour. Pour the batter into the prepared pan. Bake until a wooden pick comes out with a few moist crumbs, 45 to 50 minutes. Let the cake cool for 5 minutes in the pan before carefully flipping the cake out onto a wire cooling rack; let cool completely.

For the glaze: Place the chocolate in a medium microwave-safe bowl. In a glass measuring cup, microwave the cream until steaming, 1 to 2 minutes (do not boil). Pour the hot cream over the chocolate and let it sit for 2 minutes. Stir until the chocolate is melted and the mixture is well-combined. If there are still chunks of chocolate, microwave the mixture at 50% power in 15-second intervals until it is completely smooth.

Place the cooled cake on a serving platter. Spoon or pour the glaze on top of the cake, allowing it to drip down the sides. Decorate with sprinkles, if you like. Allow the cake to set for about 20 minutes before slicing and serving.