Concords are slipskin grapes and they have seeds. They are not difficult to work with, but you will need a food mill.
2. Pass them through a food-mill to separate the seeds, working the pulp right into the bowl with the skins. Stir in the sugar, flour, lemon zest, and juice. Taste and add more sugar if needed. Let stand until cool.
3. Preheat the oven to 400 F. Scrape the filling into the prebaked tart shell, set on a sheet pan, and bake until the filling is set, about 35 minutes. Let cool.
4. Add lightly sweetened whipped cream for serving, if desired
Sandor Katz lives to ferment; it’s his life’s work. The author of The Art of Fermentation shares how to make kombucha at home.