Place the chocolate into a heat-safe bowl and set aside.

Add half of the cold heavy cream into a bowl and whisk to soft peaks. Place into the fridge.

Add the second half of the cream into a saucepan and heat over medium heat until it starts simmering. Remove from the heat and pour the cream into the chocolate. Let it sit for 2 minutes, then whisk until the chocolate has melted and formed a homogenous consistency with the hot cream. Add vanilla, mix, and set aside.

Place the egg yolks, salt, sweetener, and water into a glass or metal bowl and place it over a pot with lightly simmering water (double-boiler). Heat, mixing consistently until the mixture reaches 71C or 160F. Use an instant-read thermometer to check.

Remove from the heat and beat on medium-high for 10 minutes with a hand mixer or a stand mixer fitted with a whisk attachment. Beat until tripled in size and pale in color.

Combine the egg mixture and the chocolate ganache until a homogenous consistency.

Add the whipped heavy cream to the chocolate mixture. Fold with a rubber spatula until fully combined, then pour into clean and dry dishes that you will use to serve the mousse (I use 4 standard size ramekins).