Blueberry cake with ricotta and polenta

Ingredients

• 230 g cane sugar
• ½ vanilla pod
• 4 eggs
• 100 g butter
• 175 g plain flour
• 75 g polenta
• 1 knife tip salt
• 1 tsp. baking powder
• ½ tsp. bicarbonate of soda
• 100 g ricotta
• 3 tbsp. finely-grated lemon zest
• 2 tbsp. lemon juice
• butter for greasing cake tin
• 2 tbsp. cane sugar for dusting cake tin
• 200 g blueberries
• granulated sugar
• icing sugar