Preheat your oven to 180 C/ 350 F . Grease your pan well with butter and generously dust with flour. Shake off excess.
Dust the blueberries with the one tablespoon flour so that they are completely covered . This is to prevent them sinking to the bottom of the pan . Keep aside.
Beat together the butter , salt , zest (if using) and sugar with a whisk or electric beater until light and fluffy.
Add the eggs , one at a time , and beat well until incorporated.
Add the yoghurt and beat well until incorporated.
Add the flour and baking powder. Mix at low speed until the flour is just incorporated.
Fold in the dusted blueberries with a spatula .
Spread batter into prepared pan and bake in the preheated oven at 180 C / 350 F for 35-45 minutes
The cake is done when a skewer inserted comes out dry . The top will be slightly browned. Cool in pan for about 30 minutes and then unmould to cool completely on a wire rack.