You'd technically be able to do this either way, however, if you've got a 1L starter going right now and decide to split it, you're only going to be pitching 500ml into each batch. That is less than the 1L starter recommended for pretty much every beer that is using a stirplate. If anything, I would step up from the 1L to a 2L and then split the starter from there.
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"Brewers enjoy working to make beer as much as drinking beer instead of working."
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