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Coat the cake tin with butter and a thin layer of flour. If needed, cover the bottom with a piece of parchment paper so the cake comes out more easily. Preheat the oven to 160 degrees Celsius or 320 Fahrenheit.
Finely grate the peel of 1 orange and squeeze the juice from 1 orange. Use a sharp knife to remove the rind from the second orange. First cut off the top and bottom and then cut from top to bottom to remove the rest of the skin and as much white as possible.
Then cut away the wedges between the membranes and cut the wedges into smaller pieces. Beat the soft butter along with 250 grams of sugar with a standmixer until it's white and fluffy.
Add the eggs 1 by 1 and only add the next one when the previous one is completely incorporated. Add the flour and baking powder and mix until smooth.
Then stir in the zest and juice of an orange. Sprinkle the orange slices with a little flour and then stir it into the batter at the end. Divide the batter evenly over the cake tin.
Bake the cake in about an hour. The cake is done if you insert a wooden skewer and it comes out clean. If the top is already starting to burn while the cake is not yet done, you can cover it with tin foil.
Make sure you open the oven door as little as possible and also carefully so the cake will not collapse. Let the cake cool in the cake tin for 10 minutes before turning it over. Then let it cool down completely. Enjoy!