Upside-Down Rhubarb Cake

I'm writing this in May and the rhubarb season has just begun. It's everywhere and people don't know what to do with it since it's got this sour taste. Well, put some sugar on it and it'll be fine! ;-)= And if you are feeling a bit creative, use flavored yoghurt in this recipe to give it a little color - because pale green and pale pink go together disturbingly well. I used Greek yoghurt with Bloody Orange flavor and since I knew it would pale too much in the oven, I added a drop of red food coloring to make it pink.

Ingredients (23x23cm pan): 

1st layer

• as much rhubarb as you need for covering the bottom of your pan
• some sugar
• butter for buttering the whole pan plus some extra underneath the rhubarb

2nd layer

• 200g flour
• 1 teaspoon baking soda
• 150g sugar
• 150g yoghurt
• zest from 1 lemon
• 2 table spoons lemon juice
• 2 eggs

3rd layer

• 2 table spoons butter
• 50g sugar
• 80g chopped walnuts

1) Butter your pan and add extra butter on the bottom because the rhubarb sticks (as you will see in the following picture, the absence of green on the top is not because I put too little rhubarb on the bottom but because some of it stayed in the pan and even thought you can easily remove it and arrange it back on the cake while it's still hot, it's too much work which can be prevented, so don't be shy and put the butter there in big blobs).

2) Peel the rhubarb (if you don't peel it, it will be pretty and pink but you will not get rid of the long "threads" it has in the skin and you will definitely feel it while eating) and sprinkle it with some sugar. It will get rid of some water this way. After that, arrange your rhubarb on the bottom of your pan.

3) Now, the second layer. Take room-temperature butter and combine it with sugar till it's lighter and fluffier. Then add the rest of the ingredients and put it on the top of the rhubarb.

4) Finish off with combining the butter with sugar and walnuts till a kind of big chunks appear. Spread the chunks on the top as you want and gently press them into the batter - some of them will stay in this layer and will create crunchy layer, some of them will sink deeper and will be still crunchy, so, it's a win :-)= but you can omit this layer altogether.

5) Put it in the oven at 150°C for about 40 minutes (I have a deep pan so it really took this long to bake the middle but if you spread it onto a larger tray, it will take shorter). As you pull it out, cover your pan with a plate and turn it around so that it falls out of the pan onto the plate and the bottom layer becomes the top layer.