Use boltz.exchange
Enter the mint top up invoice then pay with on-chain Bitcoin.
Discussion
Looks like just the thing I need, but not having any luck downloading and then verifying the Boltz Rescue Key. Won't let me proceed without a verification. 
I don't know. I've used boltz a hundred times and never had that error.
Check with their support.
Turns out, it's a bug they missed:
https://github.com/BoltzExchange/boltz-web-app/issues/846#issuecomment-2720741987
Ahh, that explains it. I've only ever used boltz on a PC.