Soft dark chocolate cake layers with tart raspberry jam filling and whipped chocolate ganache.
Preheat the oven to 350 °F. Spray three 6-inch round cake pans or two 8-inch round cake pans with non-stick spray, line the bottom of each pan with parchment paper and spray again. Set aside.
In the stand mixer bowl fitted with a paddle attachment, stir together the all-purpose flour, cocoa powder, granulated sugar, baking soda, and salt. Set aside.
Add the eggs and the vegetable oil on low until well incorporated.
Pour in the buttermilk and add brewed coffee. Mix on medium for 30 seconds. Scrape down the sides of the bowl.
Evenly distribute the cake batter among the three cake pans and bake for about 35-40 minutes or until a toothpick inserted into the center of each cake comes out clean or with just a few moist crumbs.
Remove cakes from the oven and let cool in pans for 10 minutes before inverting onto cooling racks to cool completely — wrap cakes in plastic wrap and place in the freezer to chill for 30 minutes.
In a medium saucepan, mix the raspberries, sugar, and lemon juice. Continue mixing with a rubber spatula over low-medium heat until the sugar has dissolved and the berries begin to boil.
In a small bowl, combine the cornstarch and water. Add cornstarch mixture to the boiling berries and continue to stir with a rubber spatula.
Continue cooking the mixture for 2-3 minutes until it is thickened and coats the back of a spatula.
Pour the raspberry filling into a small bowl to cool. Press plastic wrap directly onto the surface to prevent a skin from forming. Set aside to fully cool.
Add semi-sweet chocolate chips to a small microwavable bowl. In another small microwavable bowl, heat the heavy cream to a light simmer for about 1 minute.
Pour hot, heavy cream over chocolate chips. Allow chocolate to melt for 1 minute. Use a whisk or rubber spatula to mix the chocolate and cream. Mix until its velvety smooth. If chocolate is still not melted, heat in the microwave in 15-second increments.
After the chocolate ganache has cooled, add the ganache to a clean stand mixer bowl fitted with a paddle attachment. Mix on medium-high until the ganache has doubled in size and is light and fluffy. Place the ganache into a piping bag.
Remove the cake layers from the freezer and unwrap the cake layers. Next, use a serrated knife to cut off the dome of the cakes to make the layers flat and even.
Add a small amount of buttercream onto the center of the cake board. Layer the chilled dark chocolate cake, cut side up onto the cake board.
Add a thin layer of whipped ganache over the cake and pipe a circle of ganache around the edges of the cake.
Add 1/3 cup of raspberry jam filling inside the ring of ganache. Place another cake layer cut side down over the top.
Repeat the process for another layer — Crumb coat with whipped ganache and freeze for 30 minutes.
Add a thick layer of whipped ganache all over the cake. Use an offset spatula to fill in any gaps with more ganache. Then use a cake scraper to smooth out the sides of the cake. Use the offset spatula to make the top edges sharp and smooth.
Place fresh raspberries around the top edge of the cake. Serve cake at room temperature and enjoy!