Mix gelatin and cold water in the small bowl and leave it to soak. Set aside in the cold place or put in the refrigerator.
In the medium-sized saucepan add granulated sugar and turn the heat up to medium. Start melting sugar. Do not stir!
In the small saucepan add heavy gream and glucose syrup. Warm up over low heat. Do not boil!
When sugar has fully dissolved and there are no clumps left, start pouring warm heavy cream into it in 3 -4 parts. Mix with the wooden spoon and take off the heat. Please be very careful when pouring warm cream into melted sugar. The mixture will be very hot! It is important to wear heat prove gloves.
Add gelatin mass into mixture and mix well with the wooden spoon.
Strain the mixture through a sieve and let cool down.
Cut unsalted butter into small pieces. Add butter and mix well until you get smooth caramel.
Add flaky sea salt and mix again.
Transfer into pipping bag and let it set in the refrigerator for 6-8 hours or overnight.
Fill macarons.