Preheat oven to 180 C and grease a 9 inch round cake tin or a bundt pan.
Grind saffron threads in a small mortar and pestle and combine with yogurt in a large bowl. Set aside for a few minutes for the lovely yellow colour to develop through the yogurt.
Prepare rhubarb. If using frozen rhubarb (as I did) simply place the rhubarb in a small saucepan and heat. If using fresh rhubarb you may need to add a tablespoon or two of water. Stew over a medium heat, stirring occasionally, until the rhubarb is softened but still retains its shape.
Whisk the caster sugar, eggs and sunflower oil into the saffron-infused yogurt.
Sift in the plain flour, polenta and baking powder. Combine well.
Spoon the mixture into the prepared tin, smoothing over the top.
Using a slotted spoon drop pieces of rhubarb over the top of the cake batter. Reserve the gorgeous ruby red rhubarb liquid.
Bake for 30-35 minutes if using the 9 inch round tin or 45-55 minutes for the bundt pan. A skewer inserted into the centre of the cake will come out clean when it is ready.
Leave to cool in the tin for ten minutes before transferring to a wire rack to cool completely.
For the Rhubarb Icing
Sieve icing sugar into a small bowl and stir in the reserved rhubarb water. Combine well, adding more sugar if you want a thicker icing.
For the Rhubarb Saffron Sugar
Combine all four ingredients in a small saucepan. Bring to the boil and let boil for 6-7 minutes, stirring constantly.
Pour onto a silicone mat or other non-stick surface and spread into a thin layer.
Allow to cool completely before breaking into small pieces. A food processor makes short work of this.
Place cake on your cake stand, drizzle with the rhubarb icing and sprinkle with plenty of rhubarb saffron sugar.
Enjoy with a cup of tea for mid-afternoon snack!
Mum of three, daydream adventurer, OU Life Sciences graduate, occasional crafter, ex-pat Canadian & quite possibly Britain's most northerly food blogger.