I just made a batch of peanut butter thumbprints but haven't added the jam yet. Can I too them now and store in a sealed container? Will they last until Christmas? Are there food safety concerns?
No food safety concerns with cookies in general; nothing to 'go bad' as they have high sugar content (sugar and salt are both preservatives)and have been baked. If they had raw egg, that would be cause for concern, but they don't! It is true that nuts and nut oils can 'go rancid' if exposed to a long period of sunlight or hot storage conditions, but that is probably irrelevant for your cookies. Refrigerated in a tightly sealed container is the best way to store them, imo; adding the jam now won't adversely affect them.
Sorry for typo: I meant fill them now. Thanks.