My plums were from home and it is a variety that has a lot of water, maybe not the most adequate but very rich. I made two sponge cakes, one for my mother and one for me, both were delicious but the plums sank in both. The cake grows a lot and the plums, having a lot of water with the heat, were losing it. When losing weight I imagine that's why they were hidden.
The recipe is REME there you can see how I stay and in passing tell you that for me is a blog that I love and she is great, and I made some recipe for it and they are perfect and I'm sure I'll do many more ... From here I send you a thousand kisses ....

2 eggs
200 g sugar
250 g flour
200 ml of cream
100 ml of sunflower oil
1 envelope of yeast
1 tablespoon of drinking water
6 plums (my own home)
Sugar glace
butter for the mold
butter for the mold span>
We preheat the oven to 180º.
we cover a removable mold with baking paper, we spread the edges with butter, sprinkle with flour and shake a little to remove the excess flour.
Beat the eggs with the cream, oil and sugar, pour the orange blossom water, add the flour with the yeast sieved, mix well the whole and fill the mold.
Cut the plums into thick slices, and place them as we see fit and sprinkle with sugar.
We put in the oven for about 30 minutes, stick with a toothpick and if it comes out dry we remove it and let it cool on a rack.
Sprinkle with icing sugar .