Preheat oven to 325 degrees. Grease a 14-cup Bundt pan. Whisk together flour, baking cocoa, baking soda and salt in a large bowl. Combine milk and sour cream in a separate bowl.
Cream butter and sugar with a mixer until light and fluffy. Beat in eggs one at a time. Add vanilla. Reduce mixer speed to low, then alternate between adding the flour mixture and milk mixture.
Spoon batter into a pan. Bake until toothpick comes out clean, about 55-60 minutes. Let cool in pan on a wire rack, then invert cake.
To make the glaze, place chopped chocolate in a bowl. In a small saucepan, heat the cream to a simmer. Pour over the chocolate and let stand for 2 minutes. Add butter and mix until smooth. Let stand, stirring occasionally, until slightly thickened. Pour glaze over cooled cake.
Top the cake with a handful of berries and fill the center with the rest. Serve sliced with berries on the side.