Preheat the oven to 350 degrees F (180 degrees C) and grease a 9x13 inch pan.
For the cake, place the All-Purpose Flour (1 3/4 cup), Baking Soda (1 1/2 teaspoon), Unsweetened Cocoa Powder (1 cup), Granulated Sugar (2 cup), and Salt (1/2 teaspoon) in the bowl of a standing mixer and whisk until combined.
Over the stovetop, heat the Water (1 cup), Butter (8 tablespoon), and Instant Coffee (2 teaspoon) together until just melted.
Add Egg (2) and Buttermilk (1 cup) into the dry ingredients and turn the mixer on low while pouring in the melted butter/coffee mixture. Scrape down the sides, and continue to stir for another 30 seconds.
Pour batter into prepared sheet pan and bake for 20-25 minutes or until the center has just set.
Cool for about 15 minutes before removing from pan.
For the frosting, whip the Butter (1 cup) and Water (1 tablespoon) together for 2 minutes until pale. Add in the Powdered Confectioners Sugar (4 cup), Coconut Extract (1 teaspoon), and Heavy Cream (1 tablespoon) and whisk on low.
Frost the top of the cake once it’s cooled.
Top with sprinkles and cut in squares.