• For the Chocolate Cake
• Preheat oven to 350ºF. Grease and line 3 6-inch round cake pans with parchment paper. Set aside.
• In a large bowl, add the dry ingredients; all purpose flour, cocoa powder, baking powder, baking soda and salt. Whisk to combine and set aside.
• In the bowl of a stand mixer fitted with the paddle attachment, combine the softened butter, oil, sugar and brown sugar. Whisk on medium speed until creamy.
• Add the vanilla extract, eggs and egg yolk. Continue beating until fully incorporated.
• Add the dry ingredients, one cup at a time, alternating with 1/3 cup of buttermilk.
• Pour the hot water and 1 tablespoon of espresso and continue beating for another minute.
• Scrape the sides of the bowl and divide batter evenly among 3 cake pans. For exact measurements use a kitchen scale.
• Bake for 25-30 minutes (you might need more depending on your oven), until toothpick inserted in the center comes out mostly clean (some crumbs is OK). Cool cakes for 15 minutes before transferring to a cooling rack.

For the Tahini Buttercream

• In the bowl of a stand mixer fitted with the paddle attachment, beat the butter and tahini on medium speed, until soft and creamy. Reduce speed to low and add the sifted powdered sugar 1 cup at a time.
• Add the vanilla extract and 1 tablespoon of milk at a time until desired consistency (I used 2). Beat on medium-high for about 2-3 minutes. If the buttercream is too runny, add an additional 1/4 cup of powdered sugar. If it’s too thick, add 1 more tablespoon of milk.

Assemble the Cake:

• Level cakes, if needed, using a serrated knife or cake leveler. 
• Place one layer on cake stand. Spread about 1/3 of the tahini buttercream evenly on top. Repeat with the next layer.
• Place the last layer on top. Drizzle caramel on top before serving.