Preheat your oven to 325°F (160°C). Grease and line three 8-inch round cake pans, then measure out all ingredients into separate bowls.

Mix the hot water (or liquid of choice) with the cocoa powder and let it sit for a few minutes to bloom.

In the bowl of a stand mixer fitted with the paddle attachment, combine the flour, baking powder, baking soda, and salt. Mix on low speed for 1 minute.

In a separate bowl, whisk together the buttermilk, vegetable oil, eggs, and vanilla until smooth.

With the mixer on low speed, gradually pour the wet ingredients into the dry ingredients.

Scrape down the sides of the bowl, then add the cocoa mixture.

Increase to medium speed and mix for 30 seconds. Scrape the bowl and mix for another 30 seconds to ensure the batter is fully combined.

Divide the batter evenly between the prepared pans and bake for 25–30 minutes. Test for doneness with a cake tester or by pressing lightly—the surface should spring back.

Cool the cakes in the pans on a rack for 10 minutes, then invert them onto the rack to cool completely. Alternatively, while still warm, wrap the cakes in plastic wrap and freeze for later use.