You don’t have to start your draft at the beginning. In fact some people think it’s best to write the introduction after you’ve written the rest of your project. That way, you’ll avoid promising things in the introduction that you don’t get to. Or promising less than you actually have.
If there’s a part of the project that you know will be tricky or challenging, think about starting with that. Maybe chip away a bit each time you work on your manuscript. And when that section gets too challenging, turn to others that you can work on.
If there’s a part of the project that you know will be pretty straightforward to do, maybe start there. Or save that one for a day when you get stuck somewhere else.
Use placeholders. Things like “Description of research process goes here.” Using placeholders for certain parts or even certain sentences that you want to put in the draft lets you focus on finishing a section or even a paragraph without getting stuck. You can plan to remove the placeholder when you’re rested or have had time to consult sources.