Mixed Berry Crumble Cake

Directions

1. Preheat oven to 325. Grease an 8-inch-square baking pan, and/or line the pan with parchment paper if you'd like to remove the finished coffee cake from the pan before slicing.
2. Prepare the fruit filling in a small mixing bowl by tossing the berries with the first 3 tablespoons of granulated sugar, the cornstarch, and the zest of the first 1/2 lemon. Set the bowl aside while you make the crumb topping and cake batter.
3. Prepare crumb topping by first combining the melted butter with the sugars in a large mixing bowl, stirring until smooth. Add the flour gradually, stirring together with a wooden spoon. Smush the resulting stiff dough-like mixture together in the bottom of the bowl. Set aside.
4. Next, whisk the Greek yogurt, egg & yolk, vanilla extract, and zest of the second 1/2 of the lemon together in small-ish bowl.
5. In the bowl of a stand mixer fitted with the paddle attachment, combine the flour, sugar, baking soda, baking powder, and salt.
6. Add the butter and a spoonful or two of the yogurt/egg mixture, and mix on medium low speed. Once the flour is safely moistened, raise speed to medium and beat for 30 seconds.
7. Add 1/2 of the remaining yogurt/egg mixture and beat for 20 seconds. Scrape down the sides of the bowl and repeat with the last bit of the mixture, making sure the batter is well combined.
8. Spread a little more than 1/2 of the batter in the bottom of the pan, and then top evenly with the berries. Be sure to include any juices hanging out in the bottom of the bowl.
9. Apply the remaining batter to the top in small dollops, and carefully spread it around to cover the top. This does not need to be in any way perfect.
10. Break your topping mixture into crumbs and distribute evenly across the top, trying to keep them in mostly big chunks (about 1/2 inch) but including all the little crumbies as well.
11. Pop in the preheated oven and bake for 40-50 minutes. The filling will bubble through the crumbs in places, but have no fear! That's part of the cake's rustic charm. The cake is done when a toothpick inserted in the center comes out cleanly.
12. Allow cake to cool before cutting and serving. It's delicious served for breakfast or accompanied by lemon ice cream for a summery dessert. It also holds up well in the fridge for about a week (if it manages to last that long without being eaten).