Preheat the oven to 180 degrees Celsius/ 350 degrees Fahrenheit. Prepare the bundt pan (see the blog post for detailed instructions on preparing a bundt pan for baking). In short: butter the pan very thoroughly, dust it with flour and pat the pan to distribute the flour all over, including all the nooks and crannies of the pan. Shake, upside down, to remove the excess flour. If you are using a silicone bundt pan, there is no need to prepare it.

Chop the rhubarb into small cubes, place into a bowl, mix with the sugar and the cinnamon and set aside while you prepare the rest. Chop the strawberries and set aside as well.

Separate the eggs. Beat the egg whites until stiff. Set aside.

Place the soft butter, sugar, and vanilla extract into a bowl and beat until pale and creamy. Add the egg yolks, one by one, beating well between the additions.

Mix together the flour and the baking powder. Alternatively, add the flour and the yogurt to the cake batter. Carefully fold in the stiff egg whites.

Drain the rhubarb. Very carefully fold the rhubarb and the chopped strawberries into the batter.

Pour the batter into the prepared pan and bake for 55-60 minutes or until a skewer inserted in the middle of the cake comes out clean.

Leave to cool in the pan for about 10 minutes, then transfer to a wire rack and let cool completely. Dust with icing sugar, if desired, before serving.