Preheat your oven to 350°F (175°C) and prepare two 8-inch round cake pans. Grease the pans thoroughly with butter or cooking spray, then line the bottoms with parchment paper.

In a large mixing bowl, combine all-purpose flour, ground coffee or instant coffee granules, baking powder, baking soda, and kosher salt. Whisk until well blended.

In a separate bowl, cream together the granulated sugar, large eggs, and pure vanilla extract until light and fluffy. Gradually mix in the sour cream, canola oil, and firmly brewed coffee.

Pour the dry ingredient mixture into the bowl with the wet ingredients. Gently fold them together until just combined.

Divide the batter evenly between the prepared cake pans. Bake for 30-35 minutes, or until a toothpick comes out with a few crumbs. Allow cakes to cool in pans for 10 minutes before transferring to a wire rack.

While the cakes cool, whip together the unsalted butter and a pinch of salt until creamy, then gradually add confectioners' sugar and sweetened condensed milk.

Level the tops of the cooled cake layers, spread frosting on one layer, stack the second layer, and apply a thin crumb coat. Chill for 30 minutes.

Cover the entire cake with the remaining frosting and create mocha fudge swirls with chocolate sauce mixed with brewed coffee.

Slice the cake into generous pieces and serve immediately, or refrigerate until needed.