In a medium saucepan, combine the granulated sugar and water. Place it over medium heat and stir until the sugar has completely dissolved. Bring the mixture to a boil and let it cook until it reaches a temperature of 240°F (soft ball stage) on an instant-read thermometer.
While the sugar syrup is heating, place the egg yolks in the bowl of your stand mixer. Beat them on medium speed until they are thick and pale, about 5 minutes.
Once the sugar syrup reaches 240°F, carefully pour it into the whipped egg yolks in a thin stream while the mixer is running on medium speed. Continue to beat until the mixture cools down to room temperature and is light and fluffy—this could take about 10 minutes.
With the mixer on low speed, gradually add the room temperature unsalted butter, one tablespoon at a time. Once all the butter is incorporated, increase the speed to medium-high and beat until the buttercream is smooth and creamy.
Add the pinch of salt and vanilla extract (or vanilla bean paste) to the buttercream. Mix on low speed until fully incorporated.
