The first time I had proper German rhubarb cake was a Tuesday afternoon in Cologne, in a tiny upstairs kitchen above a bakery in the Belgian Quarter. Our teacher was a retired pastry baker called Frau Henrike, who pronounced everything twice if she thought you were not paying attention. The room smelled like browned butter and lemon zest, and faintly of the bakery downstairs.
How I Ended Up in a Cologne Kitchen
I booked the class on a whim. My flight had a long layover. I figured a four-hour Rhabarberkuchen class was a better use of an afternoon than another museum, and the description promised real Rhineland baking, not a tourist demo.
Frau Henrike handed each of us a striped apron and a paring knife and told us to peel the stringy bits off the thick stalks. There were six of us. Two retired German couples up from Düsseldorf, a Swedish guy who said almost nothing, me, and a woman from Birmingham who kept asking about gluten-free options.
Frau Henrike was patient with her. Patient is a strong word. Polite.
What Rhubarb Cake Actually Is in Germany
Rhabarberkuchen is not the same thing as rhubarb pie, which I had to keep reminding myself in the kitchen. There is no double crust. You have a soft butter sponge laid into a sheet pan, the fruit pressed into the surface, and a shaggy Streusel hat baked on top.
One pan. One bake. That is the whole architecture.
Frau Henrike told us rhubarb only became cake material in Europe after sugar got cheap in the 1800s. Before that, the stalks were sold in apothecaries and used as a tonic. Sour cabinet medicine.
The cake exists because someone figured out the tartness would sing if you smothered it in butter and crumbs.
A few other things I picked up in that little Cologne kitchen. The cake is traditionally a Blechkuchen, meaning a flat tray bake, not an American-style tall layered thing.
The season runs from late April to Johannistag on the 24th of June, after which the oxalic acid in the stalks gets too sharp for baking. And the leaves are toxic and always go in the bin. Always.
Bringing the Recipe Home to My LA Kitchen
Back in my own kitchen, the first problem was finding the rhubarb. It is not year-round here either. In April and May I get good thick stalks at the Wednesday Santa Monica farmers’ market from a stand I think is run by a husband and wife from Camarillo.
The stalks are deep red, almost ruby at the base, and that colour bleeds beautifully through the sponge.
The first time I made the cake at home I overcooked the Streusel. I had the pan on the top rack and walked away to make a coffee.
The crumbs went past golden into bitter. Now I bake on the centre rack, no compromises.
I also use whole milk where Frau Henrike would have used a German vollmilch, and unsalted American butter where she used a European 82 percent fat one. I tested both. The European butter is better.
I am not buying European butter every week for a Sunday cake though. The American one works. Honest.
What I Used
- 1.5 lb fresh rhubarb stalks, the reddest ones I could find at the market
- 2.25 cups all-purpose flour, divided between the cake and the Streusel
- 1 cup unsalted butter, softened, divided
- 1.25 cups granulated sugar, divided
- 3 large eggs, room temperature
- 2 tsp vanilla extract, or one packet of vanilla sugar if I have it
- 2 tsp baking powder
- 0.5 tsp fine salt
- 2 tbsp cornstarch, for dusting the batter (the German trick, more below)
- 3 tbsp whole milk
- 1 tsp ground cinnamon for the Streusel, which is a Rhineland thing
Small Twists I Have Tried
I once made this with strawberries layered in among the rhubarb. The Birmingham woman at Frau Henrike’s class would have approved. Frau Henrike was less enthusiastic.
The strawberry rhubarb pairing is an American hybrid, she said, not the German original, and the strawberries get muddy in the bake. She has a point.
I now keep it pure rhubarb at home and serve sliced strawberries on the side if I am feeling generous.
The Bake and the Saturday Afternoon Soundtrack
I usually make this on a Saturday around 3pm. Coffee already going on the stove.
The last time I made it I had Caroline Polachek on the speakers and a small plate of salted almonds I kept dipping into between steps. The whole bake takes about 75 minutes start to finish, and I get hungry.
The batter comes together fast. Beat softened butter and sugar pale, three minutes.
Eggs one at a time. Vanilla. Dry into wet alternating with milk.
The batter is thin. You spread it in a 9 by 13 pan lined with parchment and it looks meagre. That is correct.
Now the German trick. You dust 2 tablespoons of cornstarch over the batter through a fine sieve before the fruit goes on. This catches the rhubarb juice during baking and keeps the crumb from going wet.
Frau Henrike showed us this and said it was the single thing that separates an okay Rhabarberkuchen from a great one. I believe her.
Scatter the rhubarb densely across the batter. Press lightly so it sits in the surface but does not sink.
Then the Streusel goes on, made by rubbing cold butter into flour and sugar and cinnamon with your fingertips until you have shaggy lumps the size of peas and walnuts.
Not a dough. Lumps. The bigger the lumps the more dramatic the top.
45 to 55 minutes at 350. The Streusel goes deep gold.
The kitchen starts smelling like the bakery under Frau Henrike’s apartment, and you can smell the cinnamon before you see the colour change.
Cool it 30 minutes in the pan before lifting it out by the parchment overhang. The squares cut clean once it has cooled. Hot, the rhubarb still steams and the crumb falls apart on the knife.
I serve it slightly warm with softly whipped cream, the Kaffee und Kuchen way Frau Henrike insisted on. It is even better the next day, cold from the fridge, the Streusel a little softer and the tart fruit somehow sharper. That part she did not tell me, I figured it out myself.
Rhubarb Cake
Ingredients
Equipment
Method
- Preheat the oven to 350 F. Line a 9x13 inch baking pan with parchment paper, leaving an overhang on the long sides for easy lifting.
- Trim the rhubarb, peel any stringy outer skin from thick stalks, and cut into 1 inch pieces. Spread the pieces on a clean kitchen towel and let them sit while you make the batter to draw off surface moisture.
- Make the cake batter. In a large bowl, beat 0.75 cup of the softened butter with 0.75 cup of the granulated sugar on medium-high speed for 3 minutes until pale and fluffy.
- Add the eggs one at a time, beating well after each addition. Beat in the vanilla extract.
- In a separate bowl, whisk together 1.5 cups of the flour, the baking powder, and the salt. Add to the butter mixture in two additions, alternating with the milk, beating on low just until smooth. Do not overmix.
- Spread the batter evenly into the prepared pan using a rubber spatula. The layer will be thin, about 0.5 inch thick. That is correct.
- Dust the cornstarch evenly over the surface of the batter through a fine mesh sieve. This is the German trick that keeps the crumb from turning soggy under the fruit.
- Scatter the rhubarb pieces densely and evenly across the batter. Press them down very gently so they sit in the surface but do not sink.
- Make the Streusel. In a medium bowl, combine the remaining 0.75 cup flour, the remaining 0.5 cup sugar, and the ground cinnamon. Add the remaining 0.25 cup butter in small pieces. Rub the butter into the flour mixture with your fingertips until you have shaggy, pea-sized to walnut-sized crumbs. Do not work it into a dough.
- Scatter the Streusel evenly over the rhubarb, covering most of the surface but allowing a few pieces of fruit to peek through.
- Bake on the center rack for 45 to 55 minutes, until the Streusel is deep golden and a skewer inserted into the cake portion (not into a rhubarb piece) comes out clean.
- Cool the cake in the pan on a rack for at least 30 minutes. Using the parchment overhang, lift the cake out and cut into 12 squares.
- Serve slightly warm or at room temperature, dusted with a little powdered sugar if you like, with softly whipped cream or vanilla ice cream alongside.