Place half of the sugar with the water in a saucepan over low heat and bring to the boil, monitor the temperature with a cooking thermometer, the syrup should reach 244°F/118°C before being poured over the egg whites.
As soon as the syrup reaches 230F/ 110°C place the egg whites with the pinch of salt in the bowl of your stand mixer with the whisk and mix at medium speed to start, as soon as your whites are frothy, then add the other half of the sugar and switch to high speed.
Your egg whites should be firm before adding the sugar syrup.When the syrup reaches 244°F / 118°C, pour the syrup over the egg whites, drizzle in a trickle while continuing to run the mixer at low speed.
Resume mixing at high speed until the meringue has cooled (you can touch the bottom of the bowl to check the temperature for about 10 minutes).
And add the butter cut into pieces and vanilla extract to your meringue and continue blending at medium speed.
After adding the butter the texture of the cream may change, becoming more liquid or granular, especially continue mixing, your cream will be ready when it has a smooth texture.