Preheat oven to 350 degrees Fahrenheit.

Prepare two 9-inch cake pans by greasing them well with 2-3 tsp butter and dust them with 2 tbsp of flour. Tap out as much of the excess flour as possible; you only want a very thin layer to coat the inside of the cake pans so it disappears as the cakes bake.

After the cake pans are greased and floured, measure the flour, white sugar, brown sugar, cocoa powder, baking soda, baking powder and sea salt into a large mixing bowl through a sieve or flour sifter. This will help prevent lumps in the dry ingredients.

Once you've pushed the dry ingredients through the sieve, give the mixture a stir with a wire whisk to combine all the ingredients.

To a separate bowl, add the buttermilk, vegetable oil, eggs, and vanilla and whisk them together with a fork.

Set your kettle to boil some water. You'll need 1 cup.

Dump the wet ingredients into the dry ingredients and stir them together with a rubber spatula to combine. The batter will appear rough and scraggly; this is expected.

Switch to a wire whisk and very slowly pour 1 cup of boiling water into the cake batter. Add 1/4 cup of the boiling water first, whisk it in well, and then slowly add the rest. This will bring the temperature of the mixture up slowly and prevent any clumps of batter from being "cooked" by the heat of the water. Be sure to whisk the mixture gently and constantly as you add the water.

Pour the cake batter evenly into your prepared 9-inch cake pans.

Bake at 350 degrees Fahrenheit for about 30-35 minutes. After 30 minutes, if the cakes appear to be done, test the middle of one with a toothpick. If a toothpick inserted into the middle comes out pretty much clean, the cakes are done.

Remove pans from the oven and allow cakes to cool in their pan for at least an hour before removing. This will help the cakes pull away from the sides of the pan naturally and they'll be much easier to get out!

After they've cooled significantly, place a wire rack upside down over the top of each cake pan. Invert the cake pan and the cakes should slip right out, upside down, onto the wire racks. Leave them like this to cool completely.

Once the cakes have cooled completely to room temperature, wrap them in plastic wrap and refrigerate them for at least 2 hours before frosting.

Add the butter to the bowl of a stand mixer fitted with the paddle attachment. Beat the butter on medium-high speed for 1-2 minutes or until it's smooth and creamy.

Add the icing sugar and cocoa powder to the butter through a sieve or flour sifter to remove any lumps. Beat the icing sugar and cocoa powder into the butter on medium-high speed until the mixture starts to come together (it will look lumpy and a bit powdery). Add the milk and continue to beat until it looks fluffy, scraping down the sides of the bowl as needed.

Once the cakes have refrigerated for a few hours (or overnight), remove them from the fridge and remove the plastic wrap.

Slide one of the cakes onto a plate (or a cake board if you want to get fancy...but fancy isn't really what this cake is about!), making sure the cake is right-side-up. This means the bottom will be flat and the top will be slightly rounded. Since this is not one of those fancy-schmansy cakes, we're not going to bother levelling it or anything like that. It's supposed to look rustic and homemade...that's what's so beautiful about baking for someone you love.

Place a large dollop of frosting on top, in the middle of the cake using an offset spatula (a butter knife also works well in a pinch!). Carefully spread the frosting outward until it reaches the sides of the cake. Be aware of the motions you're using: don't push and then pull the frosting. This will cause crumbs on the top of the cake to lift up and become mixed in with the frosting. This is not a good look! Just be careful and spread the frosting outward and downward.

Once the top is covered, place the second cake on top of the first, but upside down (flat side up).

Place a large dollop of frosting in the middle but don't spread it yet! You'll save it for the end after you frost the sides of the cake.

Using your offset spatula, spread a large amount of frosting around the sides of the cake, making sure to fill in any holes or cracks, especially the large gap between the layers.

Once the sides are covered, spread the frosting on top of the cake, creating whatever kind of rustic pattern you like.

I chose to create small, natural-looking swirls with the same offset spatula I used to frost the cake. Carry this pattern down the sides of the cake and when you're satisfied with the way it looks, you're done!