Preheat oven to 200°C. Line a baking tray with baking paper. Sift flour and cocoa into a bowl. Stir in sugar and a pinch of salt flakes. Add the butter and, using your fingertips, rub into the flour until the mixture resembles coarse crumbs. Stir in chocolate chips and mandarin zest. Make a well in the centre and add buttermilk. Using a butter knife, stir until the mixture just comes together.

Turn onto a lightly floured surface. Knead gently, pressing dough out to 2cm thick. Using a 6cm fluted cutter, cut rounds from dough, re-kneading and cutting any scraps. Place on prepared tray, about 3cm apart. Bake for 20-25 minutes until browned and cooked through.

Transfer to a wire rack to cool. Meanwhile, for the mandarin syrup, place sugar, reserved mandarin juice and 2 tbs water in a small saucepan over medium-low heat. Cook, stirring occasionally, for 2-3 minutes until sugar dissolves. Increase heat to high. Boil, without stirring, for 3-4 minutes until syrup thickens slightly. Remove from the heat and add the mandarin slices. Set aside to cool.

Dust scones with extra cocoa powder and serve with creme fraiche and mandarins in syrup.