In the bowl of a stand mixer, beat the butter, sugar and salt together until the mixture becomes pale and fluffly. Add the eggs one by one, beating much, well blended eggs between each addition. giving the mix a really good beating before adding the next. Add 1 tbsp of the plain flour if the mix starts to look slimy rather than fluffy. Beat in the yogurt.
Mix and sift the flours before folding them into the dough. Finally add the milk, scrape sides of bowl with a spatula and beat one last time.
Lightly oil the tins with a brush and line the sides and bottom of baking paper. Divide batter between 20cm and 15cm tins (the dough should be at the same level in both tins), smooth the top with a spatula. Bake at 180°C for about 1h10mn for small cake and 1h25mn for the big. Cover the top of the cake baking paper if they brown too fast. It does not matter if the top of the cake is a little overcooked, it will cut the cake away when we assemble the cake. Cakes are done when skewer inserted into the middle should come out clean.
Prepare the rhubarb compote:
Place the rhubarb in a pan and add 25cl of water. Bring to a boil then lower the heat and cook for 25-30mn, until the rhubarb is tender and almost all the water has evaporated. Pour the rhubarb compote in a blender and blend into a smooth puree. Let cool completely.
Prepare syrup
Put the water, sugar and vanilla pod in a saucepan over low heat until sugar dissolves. Let cool to room temperature.
Prepare the Swiss meringue rhubarb buttercream:
Place the egg whites, sugar and a pinch of salt in a large bowl placed over a saucepan filled with hot water. Beat with a hand mixer until sugar dissolves and mixture is slightly hot when testing with yout finger (it must reach 70°C if you are using a thermometer). Transfer the meringue to the bowl of your hand mixer, and beat on medium speed with a whisk for 10 minutes until the bowl is completely cold. The meringue should be shiny and form a peak when lifting the whisk.
Then, reduce speed to minimum and add the butter piece by piece until it is fully incorporated. Change the whip to the beater hook, and incorporate at slow speed the cooled rhubarb compote, vanilla and a touch of pink food colouring if you want. Mix until everything is incorporated. Use the obtained icing immediately.
Assemble the cake:
When the cakes have completely cooled, turn and cut the base so that the surface is flat. Then cut into 3 layers. Put the base the base of each cake on a cake platter of the same size then soak each slice with cake syrup. Spread the rhubarb icing between each layer and then glaze the two cakes with a thin layer of icing. Let set 20 minutes in the refrigerator (cover the bowl of frosting but leave it at room temperature during that time before adding a thicker layer of icing. Smooth out with a spatula. Decorate with red fruits. Keep cool until ready to serve.
Recipe by Anne-Sophie Vidal - Fashion Cooking at https://www.fashioncooking.fr/2016/10/vanilla-cake-rhubarb-icing/