Butternut squash in Berlin
Oh, I searched, and for a long time the Vietnamese shop near Gaudystraße was my reliable source, but when they scaled back their produce selection I was out in the cold again, left to the vagaries of the Kollwitzplatz market, trolling through the half-dozen stands seeking the butternut squash I craved.
Then last Saturday, desperate to duplicate my mom's famous bhaji for Alistair and Sabine, I cycled to Helmholtzplatz more or less on a whim. Alongside the fetching little hokkaido squash at Gerd Carlsson's stand were four robust butternut squash, reasonably priced at €1.90 per kilogram; Carlsson reassured me that he has the squash in stock every week. So there you go!
After the crush of Kollwitzplatz, the Helmholtzplatz market is comfortingly small. You'll find Carlsson's stand at the northeast end beside the fishmonger's (opposite a stand that also has butternut squash, but at slightly higher prices). The Helmholtzplatz market is open Saturdays from 9 to 4 or 5.
(And because this site is already threatening to become Grapes Reified, let me also recommend - surely for a few weeks only! - the French muscat grapes also on sale at his stand.)
Update: Mid-October now, and I spotted two full crates of butternut squash in the Prenzlauer Berg BioCompany. Fingers crossed they keep stocking it, though I'll buy from Mr Carlsson as long as his supply holds out.