Butter and flour a bundt pan. If you use cocoa to flour the pan your cake will not have white streaks.
Beat butter and slowly add sugar.
Beat until the sugar is dissolved and the mixture is light and fluffy.
Add eggs one at a time, beating well after each addition.
Add vanilla and cooled chocolate.
Beat until evenly mixed.
In a large bowl mix flour, cocoa, baking soda, cinnamon, and salt.
In a 3 cup measuring cup or large bowl mix the buttermilk and the Guinness.
Add the flour mixture in three batches, alternating with the buttermilk mixture.
Spoon into a 3 quart bundt pan.
Bake for 40 to 50 minutes, or until a toothpick comes out clean.
Let cool completely.
Loosen with knife and turn out from pan, carefully.
Heat the cream up until bubbles form around the edges and the cream begins to steam.
Remove from heat and stir in the chocolate until smooth
Heat the Guinness in the microwave until it is just warm. Pour it into the ganache.
Mix until smooth and then spoon over cake.
You'll find this recipe and more at RestlessChipotle.com Guinness Fudge Bundt Cake with Guinness Ganache https://www.restlesschipotle.com/guinness-fudge-bundt-cake-with-guinness-ganache-no-beer-goggles-needed/