• Pour the contents of the two cans of mandarin oranges into a sieve or colander set over a bowl to catch the liquid. Pick out 12 perfectly shaped orange segments to use on top of the cake when it is finished. Put them into a small bowl, cover, and refrigerate them for later.

  You will need 1 cup (240 ml) of drained mandarin juice. Discard any extra. If you don't have enough, add water or orange juice to make up 1 cup.
• Preheat the oven to 350℉ (180℃). Grease the springform pan with about 2 teaspoons of butter or use cooking oil spray to grease it.

To make the Biscuitboden (base):

• Whip the egg with the 2 tablespoons of water on high speed with an electric mixer until it is pale and fluffy and about 5 to 6 times its initial volume. This will take about 3-4 minutes.
• Gradually beat in the ⅓ cup of sugar and continue beating until the mixture is thick and glossy (another 1-2 minutes).
• Add vanilla, orange zest, and 2 tablespoons of drained mandarin juice (the mixture will thin out now).
• Sift over the flour and baking powder and fold it in gently with a spatula until no flour is visible.
• Scrape the batter into the greased springform pan and spread it around evenly on the bottom. Work quickly, as the baking powder will cause the dough to get foamy and it will be a bit difficult to spread, but do the best you can - it doesn't have to be perfectly even.
• Bake for 15-18 minutes, until the cake gets golden around the edges.
• Allow the cake to cool in the pan.
• Then remove the sides of the springform pan and slide a thin spatula under the cake to loosen it from the bottom of the pan, but leave the cake in place on the base of the pan. Re-attach the sides of the springform pan to the base. Cut 2 long strips of parchment paper, about 2½-inches (6 cm) wide and 15-16 inches (38-40 cm) long. Tip: if you cut the strips lengthwise from the roll of parchment, they will curl more easily to fit the shape of the pan. Slide the parchment paper strips down into the springform pan to line the inside edges of the pan. Tuck the strips down beside the cake where possible. The paper will stick to the greased sides of the pan enough to hold the strips upright.

Make the Mandarin Cream layer:

• Put ½ cup (120 ml) of the drained mandarin juice into a small saucepan. Add the powdered gelatin and stir. Leave the gelatin to sit for 10 minutes to gel.
• Set the saucepan over low heat, stirring, until the gelatin is completely dissolved.
• Remove from the heat, and stir in the remaining 6 tablespoons (90 ml) of drained mandarin juice, 1 cup of sugar, Greek yogurt, and vanilla. Whisk until smooth.
• Whip the cream to stiff peaks in a separate bowl.
• Add the gelatin/yogurt mixture to the cream and fold to combine everything smoothly. Remove ½ cup (120 ml) of the mousse mixture and put it into a small piping bag fitted with a star tip or into a small ziptop plastic bag. Close the piping bag top with a twist tie or fold it over or seal the plastic bag. Set the bag into the fridge until it's needed to garnish the cake.
• Add the drained mandarin orange segments to the cream mixture and fold them in gently.
• Scrape the mandarin cream on top of the cake base in the springform pan, making sure the parchment paper strips stay up against the sides of the pan. Smooth the top.
• Chill the cake for 3 to 4 hours until it is set.
• Use the reserved mouse in the piping bag to pipe 12 small rosettes evenly around the outside edge of the top of the cake. If using the ziptop bag, snip off one corner about ½-inch across, and squeeze the cream out in 12 small mounded swirls. Top each rosette or swirl with one of the reserved mandarin orange sections. The cake can be covered with a cake dome and refrigerated overnight before serving.
• Cut into 12 wedges. Refrigerate any leftover cake, loosely covered, for up to 5 days.