Slice the orange into thin rounds. Add the juice and sugar to a saucepan and bring to a simmer, stirring so the sugar dissolves. Add the orange slices and cook for 10 minutes or until softened. Set aside to cool.
Make the Cake Batter
Preheat the oven to 350°F (180°C) or 160F (220F) Fan Setting. Line a 2 pound / 900g loaf tin with parchment paper letting the ends of the paper hang over the edge of the tin. Alternatively use a loaf tin liner.
Put the flour, sugar, semolina or ground almonds, baking powder, soda bicarb and orange zest in a large mixing bowl (or the bowl of a stand mixer fitted with the paddle attachment). Stir together to combine.
Add the softened butter, eggs and orange juice and beat together, scraping the bottom and sides of the bowl, until you have a smooth batter.
Bake the Orange Cake
Line the bottom of the cake tin with the cooked orange slices if you want to make an upside down orange cake.
Spoon the cake batter into the prepared cake tin and level. Bake for 55-60 minutes, or until the cake is golden, well risen and springy to the touch. A toothpick inserted in the center should come out clean.
Use the paper to lift the cake out of the tin and leave it to cool on a wire rack. Gently invert the cake onto a plate to reveal the orange slices underneath. Drizzle the cake with the orange syrup and serve.
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Notes
You can use an 8 inch round cake tin or a square one instead of a loaf pan.
Use softened unsalted butter or Stork (margarine). The butter should be soft enough for your finger to leave an imprint if prodded.
Remaining ingredients, namely the eggs and juice, also need to be room temperature.
Use a microplane to zest the oranges.
Make sure the baking powder / soda are fresh.
Check the cake five minutes before the baking time indicated in the recipe. Some ovens run hot, others are not hot enough.