Preheat oven to 350°F (175°C).

In a large mixing bowl, combine all-purpose flour, granulated sugar, cocoa powder, baking powder, baking soda, and salt.

In another bowl, whisk together buttermilk, vegetable oil, eggs, and vanilla extract.

Gradually add the wet ingredients to the dry ingredients, mixing until just combined.

Stir in the cinnamon.

Pour the batter into a greased cake pan.

Bake for 30 minutes, or until a toothpick inserted into the center comes out clean.

Allow the cake to cool.

For the glaze, heat heavy cream in a saucepan until hot, then remove from heat and add chocolate chips, stirring until melted and smooth.

Pour the chocolate glaze over the cooled cake.