Cover gelatin with 1 tablespoon of water, allowing it to bloom. Set aside.
Meanwhile, whisk egg yolks with sugar until combined and light in color.
In a small saucepan, heat milk and bloomed gelatin until it just comes to a boil. The gelatin should be dissolved at this point. Pour half of the milk into egg and sugar mixture; whisk together. Pour milk, egg, and sugar mixture into the remaining milk in saucepan. Cook on low heat until mixture thickens and holds shape on the back of a spoon.
Meanwhile, beat heavy cream to stiff peaks.
Place chocolate in medium-sized mixing bowl. Using a strainer, pour milk mixture over chocolate, and mix until incorporated. Microwave 10–15 seconds at a time if white chocolate is still solid. Add extract or essential oil. (Lemon zest will do, as well. Add lemon zest to the cream the night before and then strain before using.) Allow to cool to room temperature.
Fold heavy cream into chocolate mixture.