As the rhubarb season winds down I need to make my favorite rhubarb coffeecake one more time. After that I'll probably have to wait for another year to have it again. I really do love eating seasonally, but I'm always sad when one of my favorites fades off of the stage. And although I make liberal use of my freezer, rhubarb isn't something I freeze. Prone to exuding lots of liquid when fresh, frozen rhubarb produces a flood when cooked.
One of the reasons I like this cake so much is because of the cake itself. It is a tender yellow cake—the kind of cake that I think of when someone mentions a "crumb cake". It lacks the structure of a traditional layer cake (having one instead of two eggs) so it doesn't slice into neat, crumb-less slices. For this reason, it wouldn't make much of a layer cake—even though it's sweet, tender and moist—pretty much everything a cake should be. These qualities make it just about perfect for a coffeecake. I'm sure it would be good with other fresh fruits—sliced peaches, or maybe a scattering of blueberries or raspberries—but the layer of tart rhubarb topped by a sandy streusel is really the best.
In my rhubarb cornmeal cake post I mentioned the difficulties of using raw, fresh rhubarb in a cake. Its aforementioned tendency to release water as it cooks can make for a cake that is a gooey mess. There are several techniques for dealing with this, but one of the more interesting that I have come across was in a recipe for a rhubarb custard tart by Paula Wolfert, published in an issue of Food & Wine several years ago.
As you can imagine, rhubarb releasing its liquid into a custard as it bakes would be a disaster. To prevent this, Wolfert draws off most of the liquid ahead of time by cutting the rhubarb, tossing it with a small amount of sugar and letting it sit overnight.
The next day, so none of the rhubarb flavor is lost, the liquid is drained into a pan and reduced to a syrup.
If memory serves, Wolfert then adds this syrupy liquid to the custard base for her tart (subtracting an equal volume from the cream or milk, I would imagine). I thought this was brilliant and wanted to use it when I was working on my coffeecake recipe.
Adding the reduced liquid to a cake batter didn't seem like a great idea. Instead, I expanded her method a bit by adding the rhubarb to the sauté pan with the reduced liquid.
Doing this pulls out any remaining liquid that the rhubarb wants to give up—and if done over high enough heat reduces this remaining liquid at the same time. When you are done, all you should see is glossy, glazed rhubarb. If there happens to be any liquid left in the pan, you can just drizzle it over the cake. But try to avoid this scenario, because too much liquid tends to make the rhubarb sink into the cake. The cake won't look as nice if this happens, but it will still taste good.
Another important thing to remember when treating the rhubarb this way, is that the rhubarb and juices must cook rapidly (over high heat) and without stirring too much. The longer the rhubarb cooks, the more likely it is to become a purée. A few smashed pieces are okay, but a compote is not.
I love this cake. It is everything a coffeecake should be—tender and sweet and streusel-y with the added kick of rhubarb. I hope you will enjoy it as much as I do.
Rhubarb Streusel Coffeecake
2 c. all purpose flour
1/2 t. baking powder
1/2 t. baking soda
1 t. salt
1/2 c. unsalted butter, room temperature
1 c. granulated sugar
1 large egg
1 t. vanilla
1 c. plain yogurt (preferably not low-fat or non-fat)
Rhubarb topping (see below)
Streusel (see below)
Preheat an oven to 350ºF. Butter and flour a 13x9-inch cake pan.
Whisk the first four ingredients together in a small bowl and set aside.
Cream the butter and sugar until light and fluffy. Beat in the egg; beat in the vanilla. Stir in the dry ingredients in three additions, alternately with the yogurt in two additions.
1 lb. rhubarb, trimmed and cut into 1/2-inch pieces (about 3 cups)
1/4 c. sugar
In a large bowl, toss the rhubarb with the sugar. Cover and refrigerate overnight. Drain the rhubarb in a colander set in a sauté pan large enough to hold all of the rhubarb in a single layer. Press on the rhubarb to squeeze as much liquid into the pan as possible. Set the colander of rhubarb aside on a plate.
Bring the juice to a boil over high heat and reduce to a syrup. Remove from the heat and add the rhubarb; toss to coat. Return the pan to high heat and cook without stirring until any remaining liquid exuded by the rhubarb has evaporated. Set aside and cool to room temperature.
3/4 c. all purpose flour
6 T. sugar
3/4 t. cinnamon
3 T. unsalted butter
In a bowl, combine the flour, sugar and cinnamon; rub in the butter until the mixture looks like sand.