Preheat the oven to 325 degrees F. Butter a 12-cup or 14-cup Bundt pan. In a large bowl, combine the flour, cocoa powder, baking soda and salt. In a glass measuring cup, mix together milk and sour cream.
Pour the batter in the prepared pan and smooth top with an offset spatula. Bake until a toothpick inserted into the center comes out clean, about 50 to 55 minutes. Transfer pan to a wire rack to cool completely.
Place the chopped chocolate in a heatproof bowl; set aside. Heat the cream in a small saucepan over medium heat until it just begins to bowl. Remove from heat and pour over chocolate. Let stand one minute, then add butter and stir until smooth. Let stand, stirring occasionally until slightly thickened. Pour glaze over cake.
*Nutritional information is an estimate. Please consult a doctor or nutritionist for the most accurate nutritional info.