Preheat the oven to 180 degrees (360 F), top/bottom heat.
Meanwhile, mix together the sugar, soy yogurt, oil, lemon juice, and zest (I usually do this with my kitchen machine).
Next, add both types of flour (white flour and wholemeal flour) and the baking powder. Continue stirring.
Then stir in the blueberries
Brush the baking tin with oil and pour in the batter.
Bake on the middle rack for about 50 minutes. Do the test: poke a cake tester or sth. similar thin and long and heatproof into the cake and see if the batter sticks to it = continue baking, or not = done.
When the cake is ready, turn off the oven, open the door and let the cake cool down a bit.
For the frosting, blend the blueberries, lemon juice, and powdered sugar in a small blender. Pour the frosting over the still-warm cake to “soak” it, or over the cooled cake for a bit thicker icing.