Rhubarb rarely gets a starring role in desserts, with most recipes relying on strawberries to temper its raw, unpleasant sourness. This classic pairing, while tasty, makes very little sense to me. Rhubarb shines when gently cooked, but a hot oven destroys everything that's special about a ripe strawberry - so why do we insist on cooking them together?
When working with something as sour as rhubarb, throwing something sweet at your problem is awfully tempting, but I think embracing ingredients as they are is always a better strategy. Besides, rhubarb is delicious enough to carry a dish on its own.
It admittedly comes with several disclaimers, the most important one being that rhubarb leaves are literal poison. The stalks, while completely edible, pose their own challenges. For one thing, cooked rhubarb sure isn't much to look at. Cakes topped with a gorgeous, green-to-pink rhubarb ombré pop up on Instagram from time to time, but in my experience, the stalks usually turn a depressing shade of beige-y pink when cooked.
(Lemon juice preserves some of the shape and colour, but it's a losing battle.)
For another, the stalks are so low in pectin that rhubarb fillings readily turn to soup, soggy-ing bottoms and weighing down cakes with zero respect for you and your feelings. And, of course, rhubarb is so absurdly tart that you need an uncomfortable amount of sugar to balance it out.
I know this is a long list of drawbacks, but all I see is a list of reasons why rhubarb is the perfect fruit for baking; its glorious tartness adds a bite that no other summer fruit - except sour cherries - can touch.
Everything about rhubarb makes it a great choice for a rich, cinnamon streusel-topped coffee cake. When you're dealing with something rich and sweet, a nice punch of acidity is more than welcome, and the jammy layer of rhubarb in this recipe is bright and tart. More than a crumble or even a great rhubarb pie, this is the recipe to convert nonbelievers.
Big-Crumb Rhubarb Coffee Cake
The original recipe calls for 220 grams; I used 500 grams, and could've done with even more. If you have a lot of CSA rhubarb to deal with, double the cake and crumb ingredients - and use a bigger pan - and this will easily handle three pounds.
(Any leftover fruit can be made into a quick, delicious jam on the stovetop - or in the microwave.)
I also used a totally different filling preparation. Rather than adding cornstarch or powdered pectin, I macerate the rhubarb overnight, reduce the resulting juices to a sort of juice-based caramel, and add it back to the fruit before baking. This concentrates the rhubarb flavour and encourages the natural pectin to gel up and do its thing, so you don't need a thickener. It's my favourite way to pre-treat raw fruit for pie and cake filling.
For the rhubarb filling:
- 500g - 700g rhubarb stalks
- ½-1 cup granulated sugar
- Zest of 1 large lemon
- 1-2 teaspoons freshly-grated ginger
- ¼ teaspoon table salt
For the streusel topping:
- 1 stick salted butter
- ⅓ cup dark brown sugar
- ⅓ cup granulated sugar
- 1-2 teaspoons ground cinnamon
- Pinch of table salt
- 1 ¾ cups all-purpose flour
- Powdered sugar for dusting (optional)
For the vanilla cake base:
- ⅓ cup sour cream
- 1 large egg
- 1 large egg yolk
- 2-3 teaspoons vanilla extract
- 1 cup all-purpose flour
- ½ cup granulated sugar
- ½ teaspoons baking powder
- ½ teaspoons baking soda
- ¼ teaspoons table salt
- 6 tablespoons salted butter, very soft
First, make the rhubarb filling. Trim the stalks of their leaves and ends, then chop into half-inch pieces. Toss with the sugar, lemon zest, ginger, and salt in a large bowl; cover and rest at room temperature for at least four hours, or overnight.
When the fruit is nicely macerated, collect the accumulated juices by straining the rhubarb over a small saucepan. Return the rhubarb to its bowl, then bring the contents of the saucepan to a simmer over low heat and cook, swirling occasionally, until reduced by half.
Let cool for a few minutes off heat, then pour over the rhubarb and stir to distribute as well as you can. The rhubarb reduction will be partially caramelised and gelatinous, so it will seize up a bit when it hits the fruit. Don't sweat it; do the best you can.
Now's a good time to heat your oven to 190ºC, and make the crumb topping. Melt a whole stick of butter in a saucepan or the microwave, then stir in the sugars, salt, and cinnamon until completely combined. Add the flour and do the same. When the mixture is basically homogeneous, press it firmly into the bottom of the saucepan or bowl and set aside while you make the cake.
For the cake, whisk the sour cream, egg, egg yolk, and vanilla in a small bowl or measuring cup. Combine the dry ingredients in the bowl of a stand mixer (or a large mixing bowl, if using a hand mixer). Add a tablespoon or two of the sour cream mixture and all of the butter to the dry ingredients and mix on low speed until well combined.
Increase the speed to medium, beat for thirty seconds, then add half the remaining sour cream mixture. Beat on medium speed for another thirty seconds, scrape the bowl, and add the rest of the sour cream mixture. Beat for a final thirty seconds. Done.
To assemble, grease an eight-inch square pan (I used a nine-inch cast iron skillet and cooking spray). Scoop all but half a cup of the cake batter into the pan and smooth it out. Spoon the rhubarb and as much of the congealed juices as you can over the top. Dollop the reserved cake batter over the fruit somewhat evenly, then break the streusel topping into chunks at least half an inch long and distribute evenly over the surface.
Bake the assembled cake for fifty minutes to an hour. Due to the rhubarb, a tester is unlikely to come out totally bone dry, but when the tip of a knife or a toothpick inserted into the center comes out clean of crumbs, it's done. Cool completely before serving, dusting with powdered sugar if you like.
Distribution issues aside, that's a mighty fine dusting of powdered sugar.
Being coffee cake, this makes a great light breakfast, but I can't think of any scenario where it wouldn't be welcome. Wherever you take it, don't count on leftovers - even diehard strawberry-rhubarb lovers will freak out over this cake.