Preheat the oven to 350F and line a 9x13" pan with parchment paper.
Combine the sugar, flour, cocoa powder, salt, baking powder and baking soda in a large mixing bowl.
1 ¾ cup + 2 tablespoon white granulated sugar, 1 ¾ cup - all purpose flour, ¾ cup - dutch cocoa powder, 1 ½ teaspoon - baking soda, 1 ½ teaspoon - baking powder, ¾ teaspoon - salt
Add in the eggs, buttermilk, sour cream, oil and vanilla extract and give it a light whisk.
2 - large eggs, ⅔ cup - buttermilk, ½ cup - neutral oil, ½ cup - sour cream, 1 teaspoon - vanilla extract
In a small bowl, combine instant coffee powder, chopped chocolate and boiling water. Whisk until smooth and the chocolate is melted.
1 teaspoon - instant coffee powder, 3 oz - dark chocolate, 1 cup - boiling water
Add the mixture to the rest of the ingredients and mix until just combined.
Pour into the prepared pan and bake for 30-35 minutes until a toothpick inserted comes out with a few crumbs.
Remove from oven and let it cool completely.
To make the frosting, mix the melted butter, cocoa powder and instant coffee powder in a large bowl.
¼ cup - unsalted butter, 3 ½ tablespoon - cocoa powder, ¼ teaspoon - instant coffee powder
Mix in the warm milk until smooth. Beat in the powdered sugar slowly, with a hand mixer/stand mixer/whisk, until the frosting is smooth.
3 tablespoon - whole milk, warmed, 1 ¼ - ½ cup - powdered sugar
Spread the frosting evenly on the cake and sprinkle with some flakey salt if desired.
Cut into even pieces and enjoy!
