Preheat oven to 350° F. Grease a 8" cake pan and set aside.
In a large heatproof bowl, combine chopped chocolate and cocoa powder. Pour hot coffee over the top (see note) and whisk until smooth. Refrigerate chocolate mixture for 20 minutes.
Combine flour, sugar, baking soda, and salt in a large bowl. Set aside.
After chilling 20 minutes, remove chocolate mixture from the refrigerator. Add oil, eggs, vinegar (see note), vanilla extract, and chocolate extract (see note). Whisk until smooth.
Add the flour mixture to the chocolate mixture and whisk until smooth.
Pour batter into the prepared pan. Bake 35-38 minutes, or until a toothpick inserted in the center comes out clean. Turn/rotate cake pans halfway through baking to help ensure an even bake. Cool cake 10 minutes in the pan, then turn out onto a wire rack to cool completely.
For Strawberry Cake:
Purée the strawberries in a food processor. You should have about ½ cup of purée. Transfer the purée to a small saucepan and cook over medium-low heat until reduced to about ¼ cup. Cool completely.
Preheat oven to 350° F. Grease an 8" cake pan and set aside.
In a medium bowl, combine the dry ingredients (cake flour [see note], baking powder, baking soda, and salt). Set aside.
In the bowl of a stand mixer, combine the butter and sugar. Beat until light and fluffy, scraping down the sides of the bowl as needed.
Add the egg whites and beat until combined. Next add the sour cream and vanilla extract and mix until incorporated. Continue to scrape down the sides of the bowl as necessary.
Add half the dry ingredients and and mix until nearly incorporated. Follow with half the milk, the remaining dry ingredients, and then the remaining milk, allowing the mixer to incorporate each ingredient before adding the next. Be careful not to overmix!
Finally, add the strawberry reduction and mix just until combined. If you'd like the batter to be more colorful, you can add a few drops of pink food coloring.
Pour the batter into the prepared pan. Bake 25-28 minutes, or until a toothpick inserted into the center comes out clean. Turn/rotate cake pans halfway through baking to help ensure an even bake. Cool cake 10 minutes in the pan, then turn out onto a wire rack to cool completely.
For Vanilla Cake:
Preheat oven to 325° F. Grease an 8" cake pan and set aside.
In the bowl of a stand mixer, combine butter, coconut oil, sugar, baking powder, baking soda, and salt. Mix until light and fluffy. Scrape down the sides of the bowl as needed.
With the mixer running on low, add the egg whites one at a time. Add vanilla bean paste (see note) and mix to combine.
With the mixer running on low, alternate additions of flour and buttermilk (see note). Add half the flour, followed by half the buttermilk. Repeat for remaining flour and buttermilk, allowing each addition to incorporate before adding the next.
Pour the batter into the prepared pan. Bake 22-25 minutes, or until a toothpick inserted in the center comes out clean. Turn/rotate cake pans halfway through baking to help ensure an even bake. Cool cake 10 minutes in the pan, then turn out onto a wire rack to cool completely.
For Vanilla Bean Buttercream:
In the bowl of a stand mixer, cream butter and sifted powdered sugar until smooth. Add vanilla bean paste (see note) and cream and mix to combine.
Half of this frosting will remain vanilla bean flavored, ¼ will become strawberry buttercream, and ¼ will become chocolate buttercream. There will be more vanilla than the other flavors so you have enough to frost the vanilla cake layer and to put vanilla buttercream swirls on top of the cake.
For Strawberry Buttercream:
In the bowl of a food processor, process the freeze-dried strawberries until they become a powder.
Place ¼ of the vanilla bean buttercream in a bowl and add the strawberry powder and cream. Mix to combine.
For Chocolate Buttercream:
Place ¼ of the vanilla bean buttercream in a bowl and add the sifted cocoa powder and cream. Mix to combine.
For Assembly:
Frost cooled cake layers with buttercream. I decided to frost each cake layer with its own flavor of buttercream (chocolate with chocolate, etc.), but you can choose to frost as you desire. If storing in the refrigerator, allow the buttercream to warm before serving.Enjoy!
Notes
Note on coffee: The cake won't taste like coffee, I swear! The coffee enhances the chocolate flavor, and I highly recommend it! If you would prefer not to, you can use hot water instead.Note on vinegar: This may seem like a strange ingredient in a cake, but SCIENCE! The vinegar reacts with the baking soda (think second grade volcano science project), which gives your cake a lighter, fluffier texture. You won't taste the vinegar. That said, if you don't have white vinegar, consider taste in what you substitute. Apple cider vinegar would be a good fit, but your aged balsamic would likely lend a strange flavor.Note on chocolate extract: I highly recommend this (sometimes overlooked) extract! It lends an amazing depth of flavor to chocolate baked goods! If you can't find it in your local grocery store, you can find some here. Even better, makes yourself some Homemade Chocolate Extract for next time!Note on cake flour: Cake flour helps to lend the cakes a super soft and fluffy texture. You can substitute with all-purpose flour, but the cakes may be more dense. If you're looking to buy cake flour, you can find some here.Note on vanilla bean paste: You know me, it's in everything! Delicious and more economical than whole vanilla beans, this ingredient is my go-to for an extra punch of flavor. You can find it online here. If you prefer to substitute, you can use an equal measure of vanilla extract.Note on buttermilk: If you don't have buttermilk, you can make a quick substitution with milk (2% milkfat or greater) and vinegar or lemon juice. For this recipe, pour 1.5 teaspoons lemon juice or vinegar into a liquid measure, then add enough milk to come up to the 0.5 cup line. Let sit for 5 minutes, then it's ready for use!