Preheat oven to 350℉. Grease and flour or line with parchment paper, an 8" square or round pan. Set aside.
In a large mixing bowl, whisk together flour, sugar, baking soda, baking powder and salt.
1 ¼ cup all-purpose flour, ¾ cup granulated sugar, ½ teaspoon baking soda, 1 teaspoon baking powder, ¼ teaspoon salt
Add egg, buttermilk, vanilla and oil. Whisk together. Add hot water and whisk well until the batter is smooth. It will be runny but that's okay.
1 large egg, ½ cup vegetable oil, ½ cup buttermilk, ½ cup hot water, 2 teaspoons pure vanilla extract
Pour batter into prepared pan. Tap the pan gently against the counter to release any air bubbles.
Bake cake for 25 to 28 minutes or until golden on top and a toothpick inserted in a few places comes out clean.
Cool cake completely before frosting.
To make frosting: place butter in a medium mixing bowl and beat for 7 minutes. Add powdered sugar, ½ cup at a time and beat in well. Add heavy cream and beat in for 1 minute. Add vanilla and mix in. The frosting should be very fluffy. Spread over cooled cake. Decorate with sprinkles.
½ cup unsalted butter, 1 ½ cup powdered sugar, 1 teaspoon pure vanilla extract, 1 tablespoon heavy cream
Notes
To make homemade buttermilk: mix 2 teaspoons of apple cider vinegar with enough half-and-half to make ½ cup of liquid. Let stand for 3 to 4 minutes. When the mixture looks thick and curdled, use it in the recipe.
Use good quality vanilla as that is the primary flavor in this cake.
For the best frosting: make sure the butter is soft. Otherwise, the frosting won't be fluffy.
Please note, that the nutrition value can vary depending on what product you use. The information below is an estimate. Always use a calorie counter you are familiar with.