Preheat the oven to 180°C/350°F/gas mark 4. Grease a 25cm/10inch cast iron skillet. (Or use a cake tin)
Place the cornmeal, ground almonds, flour, baking powder, bicarbonate of soda and salt in a large bowl and whisk to combine.
Add the lemon zest, sugar, oil, lemon juice, milk, yogurt and vanilla extract and whisk well until no dry lumps remain.
Pour the batter into the prepared skillet and spread it level. Scatter over the blueberries.
Bake for about 40 minutes until a skewer inserted into the centre comes out clean or with a few moist crumbs.
While the cake is baking, mix together the lemon juice and maple syrup.
When the cake is done, drizzle over the syrup while it is still hot then allow to cool a little before serving.
The cake is best eaten on the day it is baked but will keep for a couple of days in an airtight container.