Preheat oven to 350 degrees F / 180 degrees C. Line the bottom of a 9 inch/ 23 cm cake pan with a circle of baking paper and grease well inside the pan.
In a medium bowl combine flour, salt and pudding mix.
In a large mug combine yogurt and baking soda and stir.
In another bowl combine the chopped fruits with powdered sugar and cornstarch. Stir gently so that all the fruits are covered well by the powder.
In a large mixing bowl beat together sugar and oil at high speed of the mixer, until smooth. Add the egg yolks and continue beating 3-5 minutes until the mixture thickens. Add vanilla and the yogurt with the baking soda and beat at a lower speed until homogeneous. Аdd the flour with custard and gently whisk just until absorbed in the batter. Using a rubber spatula, carefully stir in the prepared fruits.
In another bowl whip the egg whites until thick and foamy. Gently fold the egg whites into the cake batter.
Pour the batter into the prepared pan and bake for about 60 minutes or until a wooden skewer inserted in the centre comes out clean. Remove the cake from the oven and allow to cool for 10 minutes before taking it out of the pan.
When you start assembling the cake, the base should be at room temperature or refrigerated.
In a large bowl beat the cream at a high speed of the mixer until it starts to thicken. Add powdered sugar and rum extract and continue beating until hard peaks form.
In a large mixing bowl cream together butter and rum extract. Add in the sugar and keep beating at high speed until light and fluffy.
Assemble the cake:
Using a serrated knife cut horizontally the cake base into 2 equal layers (if the top is not even, level it with the knife: eat the trimmed part or break it in smaller pieces and spread it evenly over the first layer, under the whipped cream). Place one layer on a cake stand or on a large plate and spread evenly on top the whipped cream. Cover with the second layer. Spread the buttercream frosting over the top and sides of the cake. Decorate with fondant flowers.
Refrigerate for at least 2 hours before serving.
Divide the fondant into 2 parts. Colour one part with the red food colouring. Now you will have 1 white and 1 red fondant pieces. Take a small part of each piece and mix them until the new colour becomes uniform. Now you will have a second red fondant piece with less intensive colour then the first one. You can make more shades following the same process.
Using a small rolling pin roll out the fondant into thin layers. Cut out flowers with flower cutters. Place one flower on top of a sponge and press its centre with a round tool: that will make the petals look more natural.
With your hands make small balls out of the remaining fondant and press them gently in the middle of the flowers. Optionally using a toothpick make small holes in the ball to create texture.