Preheat oven to 180C. Combine almond meal, sugars, butter and 1 tsp salt in a bowl, then rub with fingertips until coarse crumbs form. Spoon half the mixture into a lightly buttered and baking paper-lined 26cm-diameter springform pan, gently pressing to evenly cover base.
Add egg, yoghurt and nutmeg to remaining crumble mixture and beat with a wooden spoon until smooth and creamy. Pour over prepared base, smooth top, scatter pistachios around edge and bake until golden (30-35 minutes.) Cool completely in pan on a wire rack to room temperature, then serve with extra yoghurt. The cake will keep in an airtight container for up to a week.