Inspired by the TH's easy to use spreadsheet, I brewed my first batch with adjustments to the mash.
I've brewed this same recipe with the same procedure 3 times before, just using straight Portland water, and each time I got 78% efficiency. This time, I added 3g each gypsum & CaCl, and my brewhouse efficiency improved to 91%. Before I get too much disbelief on the efficiency number, I don't remove trub, so it is artificially high.
Of course, this is just one data point, so I'm looking forward to repeating the experiment.
I'm wondering if the very low levels of minerals in Portland water may have some effect, as I've never gotten more than 81% on any other beer, and I generally get better efficiency with darker styles.
The recipe for 10g:
Mash at 149F for 90 min
Reason: correcting calculation error