Preheat the oven to 350º F (180º C). Grease one 8-inch round cake pan with flour-based baking spray, or grease with butter and flour, and line with a parchment paper round (cut an 8-inch circle of parchment), then grease the parchment paper. Parchment paper helps the cake seamlessly release from the pan.
In a large mixing bowl, whisk together melted butter, oil, and sugar.
Whisk in buttermilk, sour cream, and vanilla. If using coffee, dissolve the instant coffee in the hot water and add it to the mixture. If not using cofee just add the hot water. Mix until thoroughly combined.
Place a fine-mash strainer over the bowl with the wet ingredients. Sift flour, baking powder, baking soda, and cocoa powder into the liquid mixture. Add salt and whisk until combined.
Transfer the cake batter into the prepared cake pan.
Bake for 30 - 35 minutes until a toothpick inserted in the middle of the cake comes out clean with just a few crumbs attached.
Allow the cake to cool in the pan for 20 minutes before inverting it over and set it on a wire rack to cool completely.