Based on the information in Larry Hodgson's book 'Perennials for Every Purpose,' my guess would be Baptisia australis 'Alba' but since I don't grow it, I can't be certain.

Grown from seed, Baptisia generally takes several years to bloom. Given their carefree habit + attraction for pollinators, they're well worth the effort.

I went out yesterday to weed & found the tag for this a few feet away. I got the seeds as B. Leucophaea, cream babtisia. It is supposed to normally grow only 2' tall, & take extra long time from seed to bloom according to one site. This took 5 or 6 years to bloom at least, so that sounds right, but that is about all. I have white baptisia Leucantha which blooms early with other baptisias.
I think you may be right about Alba, one site says it blooms June, July, & August. This is a wee bit short for Alba, but not by a lot. It is really surprising how late it is to come up. In mid May I thought for sure it had died or I had weeded it out accidentally, but a few weeks later there it was. Of course, everything was late this year.

According to my notes, where I am B. australis normally blooms sometime in May rather than later in the growing season.

I would love to add plenty more Baptisia in my garden but thanks to winter sowing, my beds are pretty much chock-a-block full of perennials I grew from seed.

The blue baptisia australis I have blooms in April/early May. Maybe I've got some kind of new cross :) Last year when it bloomed so very late, I thought it was just because it was 1st year's bloom, & it had been a crazy hot June. When it behaved the same way this year, I decided it must be the norm for the plant.