How can this be made gluten free? Thanks so much. ;o)
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There was a pickle answer a week or so ago regarding something similar on another gratin boulangere suggested rice crackers instead of panko.
Maybe a crushed nut topping?
I would use 1/8-1/4 cup sweet rice flour, adding more until the roux looks normal. I try not to overdo the sweet rice flour because it can lead to a gummy texture, but it works really well to thicken sauces like this. You probably won't need a full 1/4 cup. Alternately, you could use tapioca starch, potato starch, or arrowroot flour to make the roux; you wouldn't need to use as much. This can affect the texture and flavor, though, so I'd try it with sweet rice flour first.
As for a panko substitute, there was a thread just a few days ago that had a bunch of suggestions. (Afraid I can't find how to search for it at the moment.) But gluten-free bread ground into breadcrumbs works really well. One of the suggestions was crushed rice crackers and I bet that'd be amazing.