Preheat oven to 180C/350F. Grease and line a 28cm X 18cm (11"X 7") rectangular pan with parchment paper, making sure paper is coming up higher than the sides of the pan. You can use a 9" round pan if you can't find a suitable rectangular one.
For the cheese filling, fix farmer's cheese with an egg, sugar, almond and vanilla extract, push it through a fine sieve to smooth it out a bit, the cheese mixture will remain slightly grainy, set aside.
For the sponge, in a mixing bowl combine eggs, butter, sugar, sifted flour, baking powder and vanilla extract and beat for 2 minutes until well combined. The batter should be light in consistency.
On a lined baking sheet spread the batter and then spoon the cheese mixture on top of it, then carefully swirl the cheese mixture with a knife.
Scatter plums all over the cake.
Bake in the oven for 45 minutes or until the cake tester comes out clean.
Cool and cut in squares. Serve dusted with powdered sugar if desired.