Chocolate Mousse Cake

Several years ago, my husband and I were on vacation in Rome, when he had his favorite dessert ever.  It was called Dios Mio Cake, or Oh My God Cake.  It was a delicious chocolate mousse, and I remember it having a cake layer at the bottom but my husband insists it was all mousse.  Regardless, despite not having the recipe I did try to recreate this heavenly dessert.  Here's what I've come up with, the mousse credited to a portion from Food Network's recipe.
[Tip: A 1 Quart container of heavy cream will be enough for both the Mousse and Ganache.  I hate it when recipes measure in cups or ounces but then the heavy cream containers say mL!]

Chocolate Mousse Cake
Serves 8-10
Prep time: 3 hours (with 2 hours to chill in fridge)

Ingredients
Cake

• 1 box chocolate cake mix; likely requires egg(s), vegetable oil, and milk to prepare

Mousse

• 8 oz semisweet chocolate (I use chips, but you could break apart a chocolate bar into 1/2-oz or smaller pieces)
• 2 1/2 cups (20 oz) heavy cream
• 2 Tablespoons granulated sugar

Ganache

• 1 1/2 cups (12 oz) heavy cream
• 2 Tablespoons unsalted butter
• 18 oz semisweet chocolate (chips or bar broken into smaller pieces)

Directions

1. Place metal bowl from a stand mixer and balloon whisk attachment in refrigerator to cool.
2. Prepare the chocolate cake according to package directions, using a 9" cake pan.  I prefer pouring the batter in just one pan and trimming off the rounded, funny looking top.  This takes 10-15 minutes longer to bake than the box directions.  You could easily prepare two small round cakes, and layer with the mousse.  I simply prefer one large cake layer at the bottom with just one large mousse layer on top.  Whichever approach you take, rub shortening on the cake pan and coat lightly with flour; tap out excess flour.  Mix cake batter, pour into pan(s), and bake according to package instructions (adding time as needed if using just one 9" pan).  Allow cake to cool, then remove from pan by inverting on a wire rack.  Let cool completely.
3. Begin the mousse by first melting the chocolate in a double boiler (or by placing chocolate in a bowl set over a pot with about 1" of boiling water.  Turn the heat down to medium, cover the bowl with plastic wrap, and let sit over the simmering water for 8-10 minutes.  Remove bowl from heat and stir chocolate until smooth.  Set aside.
4. In the well chilled mixing bowl, pour in the milk and sugar for the mousse.  Whisk using the chilled balloon whisk attachment, whisking for 1 1/2 to 2 minutes or until stiff peaks form.
5. Scoop 1/4 of the whipped cream mixture into the melted chocolate.  Use a hand whisk to gently incorporate until chocolate/whipped cream mixture is smooth and consistent.  Pour the mixture into the remaining whipped cream, and fold gently with a spatula until mousse is silky and uniform, without streaks of whipped cream or chocolate. 
6. Lightly rub the ring of a springform pan with butter or spray with nonstick spray.  Assemble the pan, then place the cake into the bottom of the springform pan. Gently scoop mousse on top.  Smooth out mousse layer, filling springform pan to the edges.  Cover with foil, careful not to touch the top of the mousse, and chill in refrigerator at least 2 hours.
7. After placing mousse cake in refrigerator to chill, make dark chocolate ganache.  Heat heavy cream and butter in a medium saucepan set to medium-high heat.  Place chocolate in a large mixing bowl.  Once cream comes to a boil, pour over the chocolate and let sit 5-10 minutes.  Gently stir the chocolate and cream mixture until smooth, preferably using a whisk.  If any clumps remain, try heating over a double boiler and stirring constantly, or microwaving at 50% power for 20-second intervals, stirring after each, until smooth.  This is very important because you will be piping some of the ganache, and if you leave any lumps the piping will not go well.
8. Once ganache is complete, reserve 1 cup and chill in refrigerator until ready to assemble mousse.  Leave remaining ganache sitting out at room temperature, covered with plastic wrap.
9. Take mousse cake out of fridge, and gently remove springform ring.  Some mousse may cling, which is ok, but if large amounts come off I like to scrape those off and smooth them back onto the cake as best I can.  Clear a large work surface, which is about to get very messy.  Pour the room temperature ganache onto the center of the mousse.  Using an offset spatula or very long, smooth knife, gently spread the ganache from the center toward the edges, allowing ganache to pour over edges.  Then smooth the edge of the cake with your spatula.  This will likely make the OCD part of you freak out.  Embrace the mess.
10. Place a star tip in a pastry bag, and scoop the chilled ganache into the bag.  Pipe on stars or other design as desired into the top and/or sides of the assembled mousse cake.  I've made a Christmas tree and monogram on different occasions.  This is why it's so important to have a lump-free ganache!
11. Very carefully slide a large flat or offset spatula under the cake, gently separating from springform pan base, and transfer cake to a serving plate or cake stand.
12. Place toothpicks at intervals on the top of the mousse, and cover with aluminum foil. The toothpicks keep the foil from touching your piped on masterpiece and that ooey gooey ganache! Refrigerate until ready to serve. 

This dessert is seriously so good, and I think well worth the effort.  It also helps that I love baking, and find this kind of prep work to be a lot of fun.  Also- be forgiving with yourself!  This thing tastes great regardless of how pretty (or sloppy) it turns out, so just roll with the punches along the way.  ENJOY!