Preheat oven to 325 degrees F. Grease and flour a deep spring-form cake pan or Bundt cake pan.
Mix together in a bowl the flour, cocoa powder, baking powder, salt, cinnamon and chili powder. Set aside.
In the bowl of a stand mixer, cream the butter and sugar until the mixture is light and fluffy, about 5 minutes. Beat in the eggs one at a time. Add in the vanilla extract and the coffee. Add in the flour mixture, alternating it with the buttermilk and combine until smooth. Pour it into the prepared pan.
Bake the cake for 70-80 minutes or until a tester inserted into the middle comes out clean. Remove to a cooling rack and let cool for 10 minutes. After 10 minutes, remove the cake from the pan and invert it onto a plate.
For the sauce:
In a saucepan over medium heat melt the 1/2 cup of butter. Stir in the brown sugar. Stir the mixture constantly until it comes to a simmer. Simmer the caramel for a few minutes then carefully add in the half and half. Stir it in and continue to simmer the caramel, stirring constantly for another 5 minutes. Remove the caramel from the heat and add in the salt.