The recipe I'm using is from Cake Journal. Although cooking sugar syrup is quite a delicate job, you will finally get there after few trials! Here is some tips I found very useful:
- Whisk to dissolve the sugar over low heat at beginning before boiling, to stop any sugar crystallize;
- After boiling, do not whisk the sugar, and turn on the heat to medium high, keep it boiling at constant speed to maintain the clear colour;
- Use a sugar thermometer is necessary, but it should normally take 5-7 minutes, and during this time, you can whisk your egg white.
Here is a video tutorial from YouTube on how to make IMBC which is step-by-step explaining the process, slightly different recipe, but same principle.