Preheat oven to 350 degrees; butter and flour a 12-cup tube pan. In a medium bowl, whisk together flour, salt, and baking soda; set aside.
Place chocolate in a medium heatproof bowl set over (not in) a saucepan of gently simmering water. Stir occasionally just until melted, 4 to 5 minutes; remove from heat.
In a large bowl, with an electric mixer, beat butter and sugar on medium-high speed until light and fluffy, 4 to 5 minutes. Add eggs one at a time, beating well after each addition; mix in vanilla.
With mixer on low speed, alternately add flour mixture in three parts and sour cream in two, beginning and ending with flour mixture; mix just until incorporated (do not overmix). Add to melted chocolate; fold to combine. Fold in cranberries.
Transfer batter to prepared pan; tap pan on countertop to level batter. Bake until a toothpick inserted in center of cake comes out clean, 60 to 75 minutes (if top browns too quickly, cover loosely with aluminum foil). Cool cake in pan 30 minutes, then turn out of pan, and cool completely on a rack.
Set cake (still on rack) over a baking sheet or waxed paper. Pour glaze over top, allowing it to drip down sides; let set about 30 minutes. If desired, arrange Cinnamon Sugar Cookies around cake, pressing in gently.