Time passes, and the Web now supplies the following recipe for lumpytums:

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Strew oatmeal into boiling milk so that it forms into small
lumps. These may be eaten with treacle and butter. Joyce Douglas
describes these as "like tiny, irregular snowballs...releasing a
puther of dry oatmeal when chewed."
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I tried it, but the oatmeal did not form lumps. The result was merely an unusually rich bowl of oatmeal (I ordinarily use water with just a little milk). As a American, I used maple syrup in lieu of treacle.

Perhaps *rolled* oats do not do the job?

Note, by the way, that "nervous" is not a mistake. According to the OED, it can mean (indeed, originally meant) "sinewy, muscular; vigorous, strong".