Heat sugar in a saucepan over medium heat until you reach a rich amber coloured caramel
Don't stir the caramel once it comes to a simmer or it can crack
Be careful not to burn
Once you have a rich caramel immediately add the butter
Next very slowly drizzle in the heavy cream and milk
Allow the mixture to boil for 1 minute
Remove from heat and allow to cool down before using
Store it in fridge