Preheat your oven to 350°F (175°C). Grease and flour a 9-inch round cake pan, or spray with non-stick baking spray. Line the bottom with parchment paper for easy removal.

In a large mixing bowl, whisk together the flour, granulated sugar, cocoa powder, baking soda, baking powder, and salt until well combined and no lumps remain.

Add the eggs, milk, vegetable oil, and vanilla extract to the dry ingredients. Beat with an electric mixer on medium speed for about 2 minutes, until smooth and well combined, scraping down the sides of the bowl as needed.

Carefully pour the boiling water (or hot coffee) into the batter. Mix on low speed until just combined. The batter will be thin; this is normal.

Pour the batter evenly into the prepared cake pan.

Bake for 30-35 minutes, or until a wooden skewer or toothpick inserted into the center comes out clean. Be careful not to overbake.

Remove the cake from the oven and let it cool in the pan for 10-15 minutes before inverting it onto a wire rack to cool completely. The cake must be entirely cool before frosting.

While the cake cools, prepare the frosting. In a medium saucepan, melt the butter over medium-low heat. Add the cocoa powder and stir until smooth, about 1 minute. Remove from heat.

Gradually whisk in the powdered sugar, milk, vanilla extract, and salt. Continue whisking until the frosting is smooth and creamy. If it's too thick, add a little more milk (1 teaspoon at a time) until it reaches a spreadable consistency. If too thin, add a bit more powdered sugar.

Once the cake is completely cool, spread the fudge frosting evenly over the top and sides of the cake. For an extra touch, you can add sprinkles or chocolate shavings.

Slice and serve your irresistible chocolate cake! Enjoy!