This chocolate mousse is made up of three components: pâte à bombe, ganache, and whipped cream. I will walk you through how to make each of them.
First, in a large mixing bowl, prepare your whipped cream. Use a hand mixer to whip your heavy cream. You do not need stiff peaks, but the whipped cream should be stable. Once you have soft peaks, set it aside.
Next, fill a heatproof bowl with your chocolate.
Then, in a saucepan, bring your heavy cream to a boil in a saucepan and then pour about ⅓ of the boiling cream over your chocolate. Mix it until all of the chocolate is melted.
Pour ⅓ more of the boiling cream into the chocolate and mix until it is combined. Repeat this process once more with the remaining ⅓ of the hot heavy cream and mix it into the chocolate ganache. Then, set it aside.
Next, prepare the pâte à bombe. Start by filling a large saucepan with water and sugar mixed together. Then, place your egg yolks in a heatproof bowl.
Heat the water and sugar in the stovetop pan to 244°F (118°C) using a thermometer. Once the pâte à bombe reaches 244°F (118°C), slowly pour it into the bowl with the egg yolks while whisking continuously (similar to how you would make an Italian meringue). Whip the egg yolks until they reach the ribbon stage (this is when the texture has thickened, the volume has doubled, and will be lighter in color/appear pale yellow). Once you’ve reached the ribbon stage, your pâte à bombe is ready.
Now you will combine your three elements (pâte à bombe, chocolate ganache, and whipped cream) to make your mousse. Begin by transferring the whipped cream into the bowl of the chocolate ganache, and then mix to combine. The reason you will mix the whipped cream into the chocolate ganache first is to lighten up the ganache texture so that it is more airy and will mix easier with the pâte à bombe.
Then, pour the pâte à bombe into the bowl of the mixed chocolate ganache and whipped cream, and fold it in until it is fully combined.