Rhubarb, Blueberry & Cherry Upside Down Cake

These fruits were not chosen on purpose. It came about by necessity. I was going to make a rhubarb upside down cake, and found I bought not nearly enough rhubarb. It wasn't the first time either: somehow, as much as I love rhubarb, I always end up overestimating the amount the stalks will yield.

What I did have, was a pint of blueberries, and little ziplock of cherries I had pitted and frozen earlier. Oh well why not. I love these fruits individually (or is rhubarb a vegetable?), all three combined should give an appetizing amount of tart and sweet. I just hoped the tart deliciousness of rhubarb would still dominate. And it does: that typical taste of rhubarb is delightfully there, balanced with the aromatic sweetness of blueberry and cherries. If you are mad about rhubarb (like me), use all rhubarb - just make sure you have enough (about 4 cups for this cake)!

I used a 10inch round cakepan. If you use a 9inch, make sure you leave it in the oven longer: it will be higher with a slightly thicker cake layer.

fruit base 
2 cups cut rhubarb
1 cup blueberries
1 tsp cornstarch
1 cup pitted cherries (frozen)
1/2 cup raw cane sugar (or regular granulated sugar if you prefer)

2 tbsp (30gr) butter
batter
2 sticks softened butter (225gr) 

1 cup granulated sugar
4 large eggs, room temperature
1 tsp vanilla extract
1/3 cup organic plain yogurt
1 tsp baking powder
2 cups flour
1 tsp salt

• preheat the oven to 325F (160C)
• Cut the rhubarb in small chunks, add the cornstarch and 1 tbsp sugar (taken from the 1/2 cup raw cane sugar). Let macerate while you prepare the rest
• butter the cake pan and line the bottom with parchment paper
• sift flour, baking powder and salt together
• add the blueberries and cherries to the rhubarb. Mix together
• in a small sauce pan, heat 2 tbsp butter and raw can sugar until melted. Pour into the prepared cake pan and divide (making sure fruits are more or less evenly distributed)
• in a mixing bowl, on medium-high beat butter and 1 cup granulated sugar until creamy (2-3 min). Scrape the sides down every so often. Add the vanilla extract.
• add the yogurt, and mix in on medium high
• add the eggs, one by one, also on medium high
• turn speed to low, and add the sifted flour, baking powder, and salt
• mix until the batter looks smooth like peanut butter. If you find it too thick, add a tbsp milk
• divide batter over the fruits carefully (do it by dividing it in dollops across the fruit, then spread with a spoon that you wet with a little water)
• bake in the preheated oven for about 1 hour. Check by inserting a metal skewer: if it comes out dry, the cake is done
• when done, take out of the oven and leave to cool for about 20 minutes (not much longer: the syrup should still be runny but not too liquid.
• carefully turn the cake upside down on a cake plate.