Preheat oven to 180C / 350F / 160C fan forced. Grease and line an 8 inch spring form tin with baking paper.
Place the semolina flour, plain flour, baking powder and salt in a bowl and whisk to combine.
Combine the orange juice, zest and vanilla and set aside.
In the bowl of a stand mixer, beat together the butter and sugar until very light and fluffy. Scrape down the sides of the bowl as required.
Add the eggs one at a time and beat well after each to combine and scrape down the bowl after each addition.
On the lowest speed or with a spatula, gently fold in 1/3 of the flour mixture, followed by 1/2 the juice mixture and repeat until all added and only just combined.
Tip the thick batter into your prepared tin and bake for 40-45 minutes until a toothpick comes out with just a couple of crumbs. After about 5 minutes remove from the tin and allow to cool completely on a cooling rack.
FOR THE ORANGE SYRUP
Pour the orange juice and sugar into small saucepan over low heat and mix gently until the sugar has dissolved. Bring to a low simmer until reduced by half.
Once the cake and syrup have cooled, prick the top of the cake with fork here and there. Pour over about half of the syrup (reserve the rest for serving). If the syrup pools in the centre use a pastry brush or spoon to spread it out.
Spread the yoghurt over the top and sprinkle over the pistachios. Serve with remaining syrup.
For best results, you should always weigh ingredients like flour and sugar. Kitchen scales are relatively cheap but if you can’t weigh the ingredients, use the spoon and level method (don’t scoop).
If the batter looks split at any point, don't worry - it will bake up fine.