Preheat the oven to 350°F. Grease and line two 9-inch square cake pans with parchment paper. This prevents sticking and helps the layers release easily.

In a large bowl, whisk together the flour, sugar, cocoa powder, baking soda, baking powder, and salt. Whisking aerates the dry ingredients and removes lumps.

Add the eggs, buttermilk, vegetable oil, and vanilla extract to the dry ingredients. Mix on medium speed until just combined. Avoid overmixing at this stage.

Slowly pour in the hot coffee while mixing on low speed. The batter will look thin, but that is exactly what gives this chocolate cake its soft, moist crumb. Scrape down the sides of the bowl.

Divide the batter evenly between the prepared pans. Use a kitchen scale for equal layers if you have one. Bake for 28 to 34 minutes, or until a toothpick inserted in the center comes out with a few moist crumbs. Cool the cakes in the pans for 10 minutes, then transfer to a wire rack to cool completely.

While the cakes cool, make the cream filling. Beat the cream cheese and butter together until fluffy and smooth. Gradually add the powdered sugar, then beat in the vanilla, salt, and enough heavy cream to make the filling silky and spreadable. Set aside.

Make the fudge frosting. Beat the butter and cocoa powder until smooth. Gradually add the powdered sugar, alternating with the heavy cream. Add the vanilla and salt, then beat on high for 2 to 3 minutes until thick, glossy, and luxuriously creamy. If the frosting is too stiff, add a little more heavy cream, one tablespoon at a time.

Place one cooled cake layer on a serving board. Spread the vanilla cream filling generously from edge to edge. Add the second chocolate cake layer and press down very gently so the filling does not squish out.

Cover the entire Chocolate Cream-Filled Fudge Cake with a seriously generous layer of chocolate frosting. Use the back of a spoon or an offset spatula to create big, swoopy bakery-style swirls.

Scatter chocolate sprinkles over the top, then refrigerate for about 30 minutes so those thick layers set before slicing. Serve slightly cool or at room temperature.