Place the chocolate into a heat-safe bowl and set aside.
Add 125ml of the cream into a saucepan and heat over medium heat until simmering. Pour the cream into the chocolate and let it sit for 2 minutes. Then, mix until the chocolate has melted and formed a homogenous consistency with the hot cream. Add the vanilla extract and salt and mix. Set aside to cool down to around 38C (100F).
Meanwhile, place the egg yolks, sugar, and water into a heat-safe bowl and place it over a pot with lightly simmering water (double-boiler). Heat, mixing consistently, until the mixture reaches 75C (165F). Use an instant-read thermometer to check the temperature.
Remove from the heat and beat on medium-high for about 5 minutes with a hand mixer or a stand mixer fitted with a whisk attachment. Whip to ribbon stage (if you lift the whisk, the pale mixture should slowly run down, leaving a ribbon on top of the mixture) or until tripled in size and pale.
Combine the egg mixture and the chocolate ganache using a rubber spatula to a homogenous consistency.
In a bowl, add 125ml of cold whipping heavy cream and whip to soft peaks, then add to the chocolate ganache. Fold in using a rubber spatula until fully combined.
Pour into clean and dry dishes that you will use to serve the mousse (I use 4 standard-sized ramekins).
Refrigerate overnight or for at least 5 hours (or freeze for 1-2 hours), or until set. Decorate with fresh raspberries, whipped cream, cocoa powder, or shaved chocolate, and serve.