A great buckle that you could just eat and eat.

Ingredients

Filling
1 1/2 cups fresh rhubarb, diced
1 1/2 cups fresh blueberries
1/2 cup white sugar
1 tbsp lemon juice
3 tbsp water, divided
2 tbsp cornstarch

Cake Batter
1/2 cup butter, softened
1/2 cup white sugar
1 egg
1 tsp vanilla extract
1/2 cup plain yogurt
1 1/2 cups all-purpose flour
1/2 tsp baking soda
1/2 tsp baking powder
1/2 tsp salt

Topping
3 tbsp brown sugar
1/4 cup flour
2 tbsp butter
1/2 tsp ground cinnamon

Directions

1. Combine rhubarb, blueberries, 1/2 cup sugar, lemon juice and 1 tbsp of water in a saucepan.
2. Heat over medium-low heat and cover, stirring occasionally, until mixture begins to boil.
3. Boil for 1 minute then reduce heat to low.
4. In a small bowl, stir together remaining 2 tbsp of water with cornstarch until cornstarch is dissolved.
5. Add cornstarch mixture to the saucepan and continue cooking until mixture begins to thicken, about 2 minutes. Remove from stove and set aside to cool.
6. Preheat the oven to 350 degrees F. Grease a 9-inch deep dish glass pan and place on a baking sheet (in case there is any buckle that overflows).
7. Beat 1/2 cup butter and white sugar in a bowl until light and fluffy. Beat in egg, vanilla, and yogurt.
8. Add flour, baking powder, baking soda, and salt then mix until just combined. Spread 2/3 of the batter into the prepared pan.
9. Pour blueberry-rhubarb filling on top of the batter.
10. Spread remaining 1/3 of the batter in small mounds on top of the filling.
11. Combine brown sugar, remaining 1/4 cup flour, 2 tbsp butter, and cinnamon in a small bowl.
12. Mix with sugar-cinnamon mixture hands until it resembles coarse crumbs.
13. Sprinkle the mixture on top of the batter and filling.
14. Bake for 35 minutes in the preheated oven or until the cake topping is golden brown.

Adapted from Strawberry-Rhubarb Buckle