Preparation

• Preheat the oven to 350°F. Combine the sugar and 1/2 cup water in a medium saucepan. Add the vanilla bean and seeds to the pan. Bring it to a boil, lower the heat, and simmer until the sugar has dissolved. Add the thin slices of sour orange and cook them for 10 minutes, until translucent. Do not boil the syrup; just gently simmer it. Remove from the heat and keep the candied oranges in the syrup.
• Combine the almond paste, 1 of the eggs, orange zest, and lemon zest in the bowl of a stand mixer. Using the paddle attachment, mix on medium-high speed until a thick and smooth paste forms. There might be some small lumps left, which is fine. Add the remaining 3 eggs. Switch to a whip attachment and whip the mixture for 5 minutes on high speed, until thick and pale in color.
• 添加the millet flour, baking powder, salt, and melted butter. Whip on high speed for another 30 seconds, until all the ingredients are incorporated.
• Line the bottom of a 9-inch round cake pan with a circle of parchment paper. Grease the paper and pan and pour in the batter. Bake for 30 minutes. When a toothpick inserted in the center of the cake comes out clean, it is done. Let the cake cool in the pan for 20 minutes. Invert it onto a cooling rack.
• Serve the cake with the candied sour oranges on top as well as some of the vanilla syrup.