Preheat your oven to 350°F (175°C). Grease and flour two 9-inch round cake pans.
In a large bowl, whisk together the flour, sugar, baking powder, baking soda, and salt.
In another bowl, mix the buttermilk, oil, eggs, and vanilla extract until smooth.
Pour the wet ingredients into the dry and mix until just combined. Don’t overdo it—lumpy is fine!
Carefully add the hot water and stir until the batter is smooth. It’ll be thin—don’t worry, that’s the magic.
Divide the batter between the pans and bake for 28–32 minutes, or until a toothpick comes out clean.
Let the cakes cool in the pans for 10 minutes, then turn them out onto a wire rack to cool completely.
Frost with your favorite vanilla buttercream or eat plain with a dusting of powdered sugar.