Sift the flour, baking powder, and sea salt into a bowl.
Beat the butter with hand-held mixer until fluffy, about 1 minute. Add the olive oil and beat at medium speed for 1 minute, until the mixture is smooth. Scrape down the bowl and beater.
Add the sugar and beat at medium speed for 1 minute.
Beat in the eggs one at a time, scraping the bowl and beaters between each addition.
Add the vanilla and almond extract and beat for 2 minutes at medium speed, until the mixture is very light.
Slowly add the flour and beat just until incorporated.
Scrape the batter into the 23 cm springform pan with a removable bottom lined with lightly buttered parchment paper and spread it out evenly using a spatula.
Arrange the plums on top in concentric circles, pressing them down into the batter. Sprinkle with Muscovado sugar and ground cinnamon.
Bake the cake in the oven at 180°C for about 40 - 45 minutes, until the edges of the plums are beginning to color and a toothpick comes out clean when inserted into the center of the cake.
Remove from the oven and let the cake cool for 10 minutes on a rack before releasing the sides of the springform. Then let it cool completely before slicing.