Step 1
Preheat the oven to 350 degrees F (175 degrees C). Grease three 9-inch round cake pans.
Step 2
Combine cocoa powder and chocolate chips in a medium bowl. Pour boiling hot coffee over top and whisk until chocolate chips have melted and mixture is smooth. Set aside to cool.
Step 3
Sift flour baking soda cinnamon baking powder and salt together in a large bowl.
Step 4
Combine sugar butter and vegetable oil in a separate bowl; beat with an electric mixer until light and fluffy. Add eggs one at a time beating well after each addition. Stir in vanilla extract. Add flour mixture in 3 batches alternating with the cocoa mixture beating batter briefly after each addition. Spread 1/3 of the batter into each prepared cake pan.
Step 5
Bake in the preheated oven until a toothpick inserted into the center comes out clean 25 to 30 minutes. Cool on a wire rack for 5 minutes. Run a table knife around the edges of each pan to loosen. Invert one layer carefully onto a serving plate and invert the remaining layers onto a cooling rack. Let cool about 30 minutes.
Step 6
Meanwhile combine sugar and salt for the caramel sauce in a small heavy-bottomed saucepan. Heat over medium-low heat stirring constantly until liquefied. Just after mixture begins to smoke slowly add half-and-half stirring constantly until fully incorporated. (Be careful as the addition of cold liquid makes the molten sugar foam up.) Remove from heat and allow to cool.
Step 7
Pour 1/2 of the caramel sauce on top of the bottom layer of the cooled cake. Add the second layer of cake top with remaining caramel sauce and add the final layer of cake. Dust lightly with powdered sugar.