Preheat oven 200c/180c fan/gas 4. Grease and line a 20cm loose bottomed round cake tin.
First make the crumble topping by placing the flour into a large bowl, rub in the butter until it resembles coarse breadcrumbs, stir in the sugar and cinnamon, put to one side.
Make the cake by first washing and drying the blueberries, sprinkle with a dusting of flour to stop them sinking.
Cream the butter and sugar until light and fluffy, beat the eggs together and add a little at a time continuing to beat, fold in the yoghurt, lemon zest, vanilla essence, apple cubes, ¾ of the blueberries, flour and baking powder.
Spoon the mixture into the prepared tin and smooth the top. Sprinkle over the crumble topping and sprinkle over the remaining blueberries, pushing down a little.
Bake for 1 – 1¼hrs until golden and a skewer inserted into the middle comes out clean.
Leave to cool a little in the tin then remove to a wire rack and cool completely.
Mix together the yoghurt, lemon zest and blueberries and serve with generous slices of the cake.