The band of less-cooked donut should be implemented in your diffuse color. Like this. This is rendered using only the diffuse effect, no specular, no displacement, no glaze.

Notice that I've got some additional small-scale color variation. I did that with a Granite node.

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Renderosity forum reply notifications are wonky. If I read a follow-up in a thread, but I don't myself reply, then notifications no longer happen AT ALL on that thread. So if I seem to be ignoring a question, that's why. (Updated September 23, 2019)