Preheat oven 180 deg C. Grease and line pan of a 22 cm (I used 20cm) springform pan with baking paper.
Combing topping ingredients in a bowl. Use your fingertips to rub until mixture resembles breadcrumbs. Chill in the refrigerator for later use.
Beat butter and sugar until light and fluffy with an electric mixer at medium speed. Add eggs, one at a time, beating well after each addition. Add vanilla, lemon zest and juice. Gradually add flour and buttermilk, alternately until mixture combined.
Spread half of the batter into prepared pan. Top with half of the blueberries and crumble mix. Top with remaining batter, smoothing the top, then top with remaining blueberries and crumble.
Bake for about 1 hour 10 mins or until a skewer inserted into the center comes out clean.
Set aside to cool in the pan for 15 minutes before lifting out onto rack to cool