Big Crumb Coffee Cake with Rhubarb

My summer fling with rhubarb continues and oh my, this coffee cake is a winner. I really should know that when Smitten Kitchen raves about a dessert, I should take it seriously. When I make this again, I'm tempted to double the cake portion and halve the crumb portion as I found myself wanting a bit more cake and a little less crumb (even though the crumb is amazing). Hopefully, I'll remember to post back if I do try the change.

One year ago: Blueberry Crumb Bars

Big Crumb Coffee Cake with Rhubarb (from Smitten Kitchen, originally NYTimes)

Ingredients
For the rhubarb filling:
225g rhubarb, trimmed
1/4 (55g) cup sugar
2 teaspoons cornstarch
1/2 teaspoon ground ginger
For the crumbs:
1/3 cup (65g) dark brown sugar
1/3 cup (75g) granulated sugar
1 teaspoon ground cinnamon
1/2 teaspoon ground ginger
1/8 teaspoon salt
1/2 cup (100g) butter, melted
1 3/4 cups (195g) flour
For the cake:
1/3 cup sour cream
1 large egg
1 large egg yolk
2 teaspoons vanilla extract
1 cup (110g) flour
1/2 cup (115g) sugar
1/2 teaspoon baking soda
1/2 teaspoon baking powder
1/4 teaspoon salt
6 tablespoons (85g) softened butter, cut into 8 pieces.

1. Preheat oven to 325 degrees. Grease an 8-inch-square baking pan. For filling, slice rhubarb 1/2 inch thick and toss with sugar, cornstarch and ginger. Set aside.
2. To make crumbs in a large bowl, whisk sugars, spices and salt into melted butter until smooth. Then, add flour with a spatula or wooden spoon. It will look and feel like a solid dough. Leave it pressed together in the bottom of the bowl and set aside.
3. To prepare cake, in a small bowl, stir together the sour cream, egg, egg yolk and vanilla. Using a mixer fitted with paddle attachment, mix together flour, sugar, baking soda, baking powder and salt. Add butter and a spoonful of sour cream mixture and mix on medium speed until flour is moistened. Increase speed and beat for 30 seconds. Add remaining sour cream mixture in two batches, beating for 20 seconds after each addition, and scraping down the sides of bowl with a spatula. Scoop out about 1/2 cup batter and set aside.
4. Scrape remaining batter into prepared pan. Spoon rhubarb over batter. Dollop set-aside batter over rhubarb; it does not have to be even.
5. Using your fingers, break topping mixture into big crumbs, about 1/2 inch to 3/4 inch in size. They do not have to be uniform, but make sure most are around that size. Sprinkle over cake. Bake cake until a toothpick inserted into center comes out clean of batter (it might be moist from rhubarb), 45 to 55 minutes. Cool completely before serving.