Put the flour, sugar, baking powder and ground vanilla in a mixing bowl. Wash the lemon and rub the peel. Then squeeze the lemons. Set aside 1 tablespoon of the juice for the icing and add the rest to the other ingredients with the zest of peel. Add the oil and soy milk and stir everything thoroughly.
Grease the muffin molds and pour approx. 1 tablespoon of the batter into the molds. Now is a good time to preheat the oven to 180 degrees top / bottom heat.
Then peel the rhubarb, cut into small pieces and fold into the remaining dough. Spread the rhubarb batter mixture on the muffin cups and bake the muffins for approx. 35 minutes.
As soon as the muffins are ready, I take them out of the oven and let them cool for about 20 minutes. I use the lemon juice and powdered sugar that I put aside to make icing, which I spread over the muffins with a teaspoon. (If the powdered sugar is a bit clumped, it is worth sifting it to make the frosting smoother.)