The correct image here is all the stuff -- oven, pans, butter, flour, salt, etc -- entering a funnel on the left and producing a baked cake on the right. The funnel itself, if you were to peer inside it, would be composed of multiple sub-funnels: pans with batter + oven as the last step, empty pans and bowls of batter as the step before that, and so on.

It's natural, not weird. The metaphor is used all the time on cooking shows, where they show you bowls of all the ingredients, and the final product next to them.