Place white chocolate in the plastic cup or bowl and semi-melt is the microwave using 20-second intervals. You can also use the double-boiler method to melt chocolate.
In the small saucepan, bring heavy cream and glucose syrup to a simmer. Do not boil!
Pour the hot mixture over the melted chocolate in 3 parts, stirring with the spatula all the time. You have to do it fast and press down. Ensure all chocolate is melted and nothing is left on the sides and the bottom of the cup or bowl.
Emulsify ganache with a hand blender. Add unsalted butter and salt. Emulsify again for 5-10 seconds. The ganache should be smooth and silky.
Transfer the ganache into a flat container or bowl and cover it with the plastic wrap "to contact."
Refrigerate ganache for 6-8 hours, ideally overnight. Please note that White Chocolate Ganache is stabilizing longer than dark or milk chocolate.
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Notes
Use good-quality white chocolate. The ratio of heavy cream to chocolate will change depending on the cocoa butter percentage in the chocolate.
Use an emulsifier blender to make ganache; do not skip this step.
When you are ready to fill macarons, I recommend removing the ganache from the fridge about 30 minutes before and keeping it at room temperature.