Chocolate Cake 

1. Preheat the oven to 350F(175C). Grease and line the base of an 8 or 9-inch springform pan with parchment paper. I used this baking pan to make mousse cake.
2. In a medium mixing bowl, add the flour, cocoa powder, baking powder, baking soda and salt. Whisk ingredients together to combine.
3. In the bowl of stand mixer fitted with paddle attachment or with a hand-held electric mixer and large mixing bowl, add the oil and sugar. Mix ingredients together at medium high speed to combine, about 1-2 minutes.
4. Next, mix in the yogurt into the oil-sugar mixture to combine, about 1 minute.
5. Beat the egg into wet batter at medium high speed until fully incorporated, about 30-60 seconds.
6. Reduce mixer speed to low. In an alternating fashion, starting and ending with the dry ingredients, mix half of the dry ingredients into wet batter followed by the coffee and vanilla extract and ending with the remaining dry ingredients.
7. Stop the mixer and use a rubber spatula to scrape the sides and base of the bowl to catch any unmixed ingredients.
8. Resume mixing cake batter at medium speed for an additional 30-60 seconds. The resulting batter should be slightly thick and smooth.
9. Spoon cake batter into prepared baking pan.
10. Bake cake batter rotating the pan halfway through bake time for 24-26 minutes or until a toothpick inserted into the center of the cake comes out clean.
11. Cool cake in the pan until it reaches room temperature, about 45-60 minutes.
12. Once cooled, level the cake by cutting off the domed top with a serrated knife or cake leveler.
13. Return leveled cake back to springform pan. 

Chocolate Mousse

1. In a small mixing bowl/dish, add the cold water and sprinkle the gelatin over the top of water. Allow gelatin mixture to rest for 5 minutes as it absorbs the water and takes on a gel-like consistency.
2. Add the egg yolks and sugar into a medium mixing bowl. With a hand whisk, mix ingredients together until mixture appears slightly thickened, about 2-3 minutes.
3. In a medium saucepan, add 1 cup of the heavy cream and warm up under medium heat until visible stream starts to come off the surface and small bubbles are forming along the outer rim of the cream, about 1-2 minutes. You only want to heat up the cream here and not bring it to a full boil.
4. Slowly whisk the heated cream into egg mixture in a slow steady stream.
5. Pour egg mixture into a medium saucepan and cook under medium low heat until it reaches the consistency of slightly thicken custard cream and coats the back of a spoon, about 4-5 minutes. If you have a kitchen thermometer, custard should register between 167-170F (75-77C) before removing from heat.
6. Pass custard through a sieve into a medium mixing bowl.
7. Next, whisk in the dissolved gelatin followed by the finely chopped chocolate and vanilla extract into custard. You will end up with a smooth, chocolate mixture.
8. Allow chocolate custard to cool at room temperature until no longer warm to touch, about 30-40 minutes. As chocolate mixture cools, whisk it every 10-15 minutes to help prevent a skin from forming on the top surface.
9. As chocolate mixture cools, pour the remaining cold heavy cream into a large mixing bowl.
10. Using a hand whisk or electric mixer, whisk the cream until it starts to thicken and form very soft peaks. The goal here is not to whisk the cream until it has stiff peaks. When you lift up the beaters/whisk, the peaks of the cream should drop down and not stand upright.
11. Fold half the soft cream into the cooled chocolate mixture until thoroughly combined. Repeat with remaining cream.
12. Spoon chocolate mousse over cooled, leveled chocolate cake. Spread chocolate mousse into an even layer using an offset or regular spatula.
13. Gently tap springform pan against a hard surface 1-2 times.
14. Refrigerate chocolate mousse cake for 4-6 hours or overnight to set.
15. Place chocolate mousse cake in the freezer for a minimum of 30 minutes before assembly. 

Chocolate Ganache Glaze 

1. In a large mixing bowl, add all of the finely chopped chocolate.
2. In a medium saucepan, add all of the heavy cream and warm up under medium heat until visible stream starts to come off the surface and small bubbles are forming along the outer rim of the cream, about 1-2 minutes.
3. Alternatively, cream may be warmed up in the microwave on high at 30 second intervals.
4. Pour heated cream over chocolate and allow chocolate-cream mixture to sit untouched for 1 minute.
5. Whisk cream into melted chocolate until all of the cream is incorporated into chocolate and you have a smooth, shiny chocolate ganache.
6. Next, whisk softened butter into chocolate ganache (optional but highly recommended for extra shiny ganache). 

Whipped Chocolate Buttercream Frosting 

1. In the bowl of a stand mixer fitted with paddle attachment or with a hand-held electric mixer and large mixing bowl, cream the butter and salt at medium high speed until smooth and fluffy in appearance, about 2-3 minutes.
2. Reduce mixer speed to low and mix in the confectioners’ sugar and cocoa powder into creamed butter. Gradually increase mixer speed back to medium.
3. Once all the dry ingredients have been incorporated into creamed butter, mix in the vanilla extract and 2 tablespoons of heavy whipping cream into buttercream until fully incorporated.
4. If buttercream appears to be on the soft side, mix additional confectioners’ sugar 1/4 cup at a time until a thick but pipeable consistency is reached.
5. If buttercream appears too thick, mix in remaining heavy whipping cream, 1 teaspoon at a time until the desired consistency (thick but pipeable) is reached.
6. Increase mixer speed to medium high and mix chocolate buttercream frosting for an additional 30-60 seconds. The resulting frosting should be smooth and fluffy in appearance.

Assembly

1. Line a large baking sheet with parchment paper. Set a small bowl in the center of the parchment lined baking sheet.
2. Retrieve chocolate mousse cake from the freezer. Run warm water over a clean kitchen towel and squeeze out excess water.
3. Use the heated kitchen towel to wipe the sides of the chilled baking pan. Repeat this process 2-3 times. This will help loosen the mousse cake from the pan.
4. Remove cake from springform pan and set over the small bowl on parchment lined baking sheet.
5. Working quickly, pour slightly cooled chocolate ganache over mousse cake. Use offset spatula to help spread glaze over and down the sides of the cake.
6. If parts of the cake are missing glaze, simply use offset spatula or spoon to apply some of the excess/remaining glaze to those areas so that cake is completely covered in chocolate glaze.
7. Allow glaze to set for 10-15 minutes in the fridge.
8. As glaze sets, fill a large pastry bag fitted with preferred pastry tip with the chocolate buttercream. I used a 8B Wilton pastry tip.
9. Pipe medium-sized dollops of buttercream over the top of glazed mousse cake.
10. Sprinkle or evenly place chocolate pearls over piped frosting (optional).