A moist cake with tart apples, scented with cinnamon and lemon zest, dusted with sugar. The companion to four-o'clock coffee in Hilbert's academic Göttingen.

Why this dish? In Göttingen, where Hilbert taught for nearly forty years, scientific life happened as much around blackboards as around coffee tables and walks. The ritual of Kaffee und Kuchen structured the afternoons of university families—an apple cake, a discussion of the infinite.

In Göttingen, the afternoon belonged to coffee and cake—it was there, over a slice of Apfelkuchen, that we solved more problems than at the blackboard, believe me. The apples from the orchard, nice and tart, the cinnamon, a lemon zest: nothing complicated, but everything must be right. Wir müssen wissen, wir werden wissen—we must know, we shall know—but first, a good slice of cake and a walk.

How it was made : Without widespread baking powder, egg whites were often beaten to a stiff peak to aerate the batter; sugar, more costly, was used sparingly. Local tart apples (reinettes) were preferred, and cinnamon remained the most common festive imported spice.

The contemporary twist : Arrange the apple slices in a regular spiral like a mathematical curve: a 'Hilbert spiral' Apfelkuchen for a wink.

David Hilbert · Charactorium