Rhubarb-blackberry coffee cake

Happy 4th of July, all! I don't know how to modify this blogger site in protest, so I made something tasty instead. This is half rhubarb from Lester's garden (the first two ripe stalks!), half foraged blackberries that we froze since last summer, and just a few cape gooseberries from the garden for good measure. It's vaguely red-white-and-blue, but it more reminds me of Alan and Lester talking about British summertime baking—my kind of celebration. And the crumble top is friggin amazing.

filling:
1/2 lb tart fruit (eg rhubarb, blackberries, cape gooseberries)
1/3 c sugar
2 t cornstarch
1/2 t ginger

Prepare the fruit (chop the rhubarb, defrost the blackberries, etc). Toss everything together and set aside.

crumble:
1 stick salted butter, melted
1/3 c turbinado sugar
1/3 c sugar
1 t cinnamon
1/2 t ginger
1 3/4 c flour

Stir the sugars and spices into the melted butter until the white sugar is dissolved, then stir in the flour until it's firm and crumbly but thoroughly moistened. Set aside.

cake:
1 c flour
1/2 c sugar
1/2 t baking soda
1/2 t baking powder
3/4 stick softened butter, cut into pieces
1/3 c yogurt
1 egg
2 t vanilla extract

Stir together the dry ingredients (flour through baking powder) in a medium bowl. Stir in the butter, kind of like biscuit dough. Mix the wet ingredients (yogurt through vanilla) in a small bowl then stir into the dry ingredients in two batches.

assembly:
Preheat the oven to 325F and butter a 8" square pan. Spread the batter evenly in the bottom of the pan and top with the fruit. (Smitten Kitchen said to leave a bit of batter aside and dollop it on top of the fruit, which I did, but I don't think it makes much of a difference.) Sprinkle the crumble over the fruit, breaking up large chunks and squishing together sandy bits to make roughly 1/2" crumble bits. Bake for 50 min until a toothpick comes out clean.