Ernie gives a lecture.
I love the unself-consciousness of this sketch, the assumption that it's a perfectly natural and normal thing for Ernie to be giving lectures in his kitchen, and therefore it requires no explanation, even though he's never (to my knowledge) done it before or since.
I just noticed that Ernie takes that baking sheet out of the oven without any sort of oven mitt or potholder. Oops. Maybe it's like a cooking show and he pre-made the cookies earlier.