Preheat your oven to 350 degrees and grease two 8 inch round cake pans. Optionally line the pan with parchment paper and set aside. In a large bowl, whisk together the flour, sugar, baking soda, and salt. In a microwave safe medium bowl, melt the butter until just melted in the microwave, about 2 minutes. Then add in the coffee and microwave for another minute, or until the mixture is just boiling. Stir in the cocoa powder and whisk to combine until smooth.

Pour the hot chocolate mixture over the dry ingredients, and whisk until combined- the mixture will be very thick at this point, and it doesn't have to be fully mixed through. Then stir in the buttermilk, eggs, and vanilla extract and whisk until combined and smooth. Pour the batter into your prepared cake pans, and bake for 30-35 minutes, or until a toothpick comes out with just a few crumbs clinging to it, or an instant read thermometer reads 200 degrees when inserted in the center of the cake. Cool the cake completely before frosting it. Optionally, remove the cakes from the pans while hot and wrap tightly in plastic wrap, allowing the cakes to cool at room temp while wrapped. See tips on this process above.

In a small saucepan, stir together the flour and milk and cook this mixture over medium heat until you have a very thick paste. It should take about 5 minutes, whisking constantly to avoid lumps. This mixture needs to cool completely to room temperature before moving on- don't skip the cooling process! It's important.

In a large bowl or the bowl of a stand mixer, beat together the butter, sugar, and espresso powder for about 10 minutes, or until the mixture is extremely fluffy and lightened in color. Add in the completely cooled flour paste mixture, and whip for 5-10 minutes, or until you have a very light, fluffy frosting mixture. Beat in the salt and vanilla extract until well combined, and then frost your cake as desired.

I like to slice the cake layers to remove any domed tops, and then do a simple cake-frosting-cake-frosting layering process. Level cakes will make the process much neater and easier. I use a sharp serrated knife and work slowly around the cake to slice off the top until you have an even layer. Going slowly helps!

Slice and enjoy!