In a microwave-safe bowl, melt white chocolate in a microwave. (Or you can use a double boiler.) For the microwave, set it for 1 minute at 50% power (for 1000watt microwave!).
Stir well and put it back for 15-30 seconds at 50% power, depending on the consistency. (If it looks pretty solid, put it for 30 sec, and if it started melting - for 15 sec.)
Then stir well and put it back for another 15 seconds at 50% power, if needed, or until the chocolate is completely melted, stirring well every 15 seconds.
Place the cream in a small saucepan.
Warm it up over medium heat until you see small bubbles around the edges. No need to scald/boil it.
Add 1/3 of cream into melted chocolate and stir gently with a spatula, or a whisk. It'll look grainy and seized, but don't worry.
Stir in another 1/3 of cream and mix until almost smooth. Then add the last of cream and it should turn silky smooth.
Optional, but highly recommended: Blend the ganache with an immersion blender for 30 seconds. This creates better emulsion and smoother ganache!
Transfer the ganache into a flat container, or a baking pan (it helps to set the ganache quickly!).
Cover with plastic wrap, touching the entire surface of the ganache to prevent any skin forming.
Refrigerate for at least 5 hours, or overnight, to thicken and stabilize the ganache. After the chilling time, ganache should be nice and thick, and hold its shape when piped.
Stir the ganache with a rubber spatula to soften it and restore the shine.