Preheat oven to 175°C (350°F).
Generously grease a 23-24 cm (9-9.5-inch) springform pan with butter. Sprinkle pan with 3 tbsp. demerara sugar, make sure to get some on the sides of the pan aswell.
Melt butter and stir in the yogurt. Set aside to cool.
Wash and slice 1-2 blood oranges thinly. Remove any seeds. Put the slices in a single layer in the bottom of the pan.
Beat the eggs, sugar and vanilla until very light in color and texture, about 2-3 minutes.
In a medium bowl, mix flour, baking powder and salt. Gently stir the flour mixture into the egg mixture. Add the butter mixture and zest to the batter and stir until smooth.
Pour the batter into the prepared pan and smooth the top with a spatula.
Bake for 32-36 minutes (but start checking around 25 minutes) until cake is golden brown on top and a cake tester comes out clean.
Let cool for 5 minutes before inverting the cake onto a rack or a plate to cool completely. Serve with the cardamom+almond ice cream from my previous post, or vanilla ice cream – or simply eat it as it is!