https://www.homebrewtalk.com/f127/berliner-weiss-many-ways-385934/
Personally:
First sanitize everything. This won't be boiled for at least 3 days.
50/50 Pilsen/Wheat
Mash in @145F for 45.
Cool to 120F leaving grains in.
Throw 2 handfuls of unmilled grains, cover mash with sanitized saran wrap.
Put under a heat lamp for 5 days. (very sour) Longer you leave it the more sour it gets. (to a limit of course, ph can only lower so much from lacto) Taste as it sours the first time to gauge what timeframe is right for your tastes. It gets a bit more sour after carbing.
Collect wort, bring to boil for 20 minutes.
.5 tettnang @ 15 minutes.
Pitch US-05, keep around 64F.
Fermentation start lags due to low ph, this is normal.
After primary bottle with ~ 3 CO2 volume, or rack to secondary with fruit for a week and then bottle.
Creates a really clean sourness with 3-4 week turnaround.
I use grains for lacto because it supposedly gives a better sourness. You can do it without a heat lamp as well, just takes longer to sour.
Keeping oxygen out during souring is the most important part by far. It will create horrible flavors.
Some like to collect the wort and sour that instead of the mash, works well according to forum posts.
Some like to ferment with brett, it works very well in low ph and if it's done as the primary fermentation by itself it works much more quickly and can finish in 1-2 weeks. I'm planning on doing this very soon, interested in the difference.
But check out that thread for more detailed info and more first hand reports. Personally I've had excellent results with my method and don't intend to change much besides trying brett in place of sacc.