Preheat the oven to 350°F. Coat a 10-inch (10-cup) bundt pan with nonstick baking spray.
Melt 2 ounces chocolate according to the package's directions. Chop the remaining chocolate.
Sift the flour, cocoa powder, cinnamon, cardamom, baking soda, and salt into a large bowl. Whisk the sour cream and coffee in a medium bowl.
Beat the butter and brown sugar with an electric mixer on medium-high speed until smooth, pale, and fluffy, about 5 minutes. Scrape the bowl, add the melted chocolate, and beat on medium speed until smooth. While beating, add the eggs one at a time and then the vanilla, beating well after each addition.
Scrape the bowl and beat on low speed. While beating, add the flour mixture in thirds, alternating with two additions of the sour cream mixture. Scrape the bowl and beat until smooth. Fold in half of the chopped chocolate (3 ounces), then spread evenly in the prepared pan.
Bake until a skewer inserted in the center comes out clean, 50 to 55 minutes. Cool for 10 minutes on a wire rack, then invert onto the rack to cool completely.
Heat the cream in a small saucepan over medium heat until bubbling. Remove from the heat and add the remaining 3 ounces chopped chocolate. Stir until smooth. Pour the glaze slowly over the cake on the rack. Top with sprinkles if you'd like. Let stand until the glaze sets.