Wash the plums and peel them. I had smaller plums and left them in halves. If they are bigger, cut them into quarters. Sprinkle 2 tablespoons of sugar on them and leave them in a bowl. Separate the yolks from the whites. In a deep bowl, beat the egg whites with a salt mixer. Beat the yolks in another bowl with cold water for 1-2 minutes. Add the sugar and beat for another 2-3 minutes.
Add the oil and mix gently until incorporated and then pour the sifted flour and mixed with baking powder. Incorporate the egg whites and mix gently with a wooden spoon, from bottom to top. Pour the resulting composition into a tray lined with baking paper.
Place 5-6 crushed biscuits on top and place the plums and sprinkle with cinnamon. Put the cake in the hot oven and bake at 180 degrees C for about 40 minutes. When it is browned, take the tray out of the oven and let the cake cool for 20 minutes. Turn the cake over on a wooden bottom and sprinkle over the 5-6 crushed biscuits for decoration. Good appetite!