[Plane]

You could just purchase the lowest possible level of Burning Attack (that's either 1 damage for 0.25 dice or 1d-3 for 0.1 dice) and then use Extra Effort to boost the level.

To reflect higher magery allowing for higher damage, we know Magery is a Talent so just allow Talent to add to Will rolls for extra effort?

Powers 160 actually doesn't mention this like 172 (Temp Enhance) or 173 (abilites at default)

Maybe to keep it canon, 173 is the better approach: treat Magery 0 as the 5pt base advantage (since it isn't a talent) and the 1+ as bonuses to your UAAD roll.

"-2 per 25% of the starting ability’s point cost the default ability is worth" is convenient here: Burning Attack's usual base cost of 5 (same as Magery) for 1d drops down to 25% if it's a fixed 1 damage.

You could offset than -2 more easily with higher levels of Magery talent to influence this roll. Subsequently you might then use "Extra Effort" to boost the levels of your sword once you've gained it, though as mentioned before that doesn't benefit from Magery, so it could be better to make it strong to begin with.

RAW it seems like you could even make it 0.1 (1d-3) but I think there should be some kind of house rule that penalties must be less than dice for non-crushing attacks due to them getting minimum damage of 1 regardless of penalties. About the only drawback is that you need to EE-boost it 10x to get 1d instead of 10/3x.