I swear this is a once in a lifetime boost that I've tried to replicate to no avail:

I had to have been perfectly on the line between the "ice" section oaf the track and the normal section when I released the tiny bit of boost meter I had from the start. This seems stupid precise as releasing the boost too early starts it and ends it when you touch the "ice" or you lose it by touching the ice without releasing. I just don't know if this run can be beaten without it.

Image for reference:

The frame before the boost releases, meaning I had already released my left trigger and miraculously timed it so the boost released on the line.