Preheat the oven to 200°C. Grease a large baking sheet with non-stick spray or line with baking paper.
1. Sift the dry ingredients three times, then mix in the sugar. Rub the butter in until the mixture looks like fine breadcrumbs. Lightly fold in the berries and lemon zest.
2. Whisk the yoghurt, egg and vanilla essence. Cut into the flour mixture using a metal spatula or a flat- bladed knife until just combined – don’t overmix.