Black Velvet Cake

Name: Black Velvet Cake
Prep time: 45 min
Cook time: 32 min
Total time: 1 h 17 min
Cuisine: American
Ingredients: 2 Cups (165g) all purpose flour; 1 2/3 Cups (340g) granulated sugar; 2/3 Cup (80g) black cocoa powder; 2 tsp baking soda; 1 tsp baking powder; 1/2 tsp salt; 1/2 Cup (120ml) vegetable oil; 2 large eggs, room temperature; 1 1/2 tsp pure vanilla extract; 1 Cup (240g) full-fat buttermilk*, room temperature (DIY recipe in notes); 1 Cup (240g) hot coffee or hot water; 2 Cups (452g) unsalted butter, room temperature; 7 Cups (840g) powdered sugar; 1/2 Cup (60g) black cocoa powder; 1/2 Cup (40g) natural unsweetened cocoa powder; 6 Tbsp whole milk, room temperature; 4 tsp pure vanilla extract; 1/4 tsp salt, or to taste; 2 1/2 tsp black food color gel**