Preheat the oven to 350°F.

Boil 2 whole cara cara oranges for 20 minutes changing the water halfway through (easiest to have two pots of boiling water). 

While the oranges are boiling, prepare the upside down topping. Line a 9 inch cake pan with parchment paper and fold the paper inward along the sides so it hugs the curved edge of the pan. Spray with non-stick cooking spray.

Microwave ½ cup sugar and ¼ cup water for about 45 seconds or until the sugar fully dissolves. Cut the other 2 cara cara oranges into ¼ inch slices, being mindful to keep the peel on. Once sliced, use a paring knife to remove the peel from each slice. Pour half of the sugar mixture into the cake pan, then arrange the orange slices to cover the bottom of the pan. Once the oranges are arranged, pour the remaining sugar mixture over the orange slices. 

Once the oranges are finished boiling, rinse them under cool water so they are cool enough to touch. Slice the oranges into ¼ inch slices, dice them, and remove any seeds. Place oranges in a food processor and pulse for about a minute, scraping the sides down every 10 seconds. Add in sugar, eggs and vanilla extract and pulse for 10 seconds until combined. Finally add in baking powder and almond flour and pulse for another 10 seconds until combined.

Pour into the prepared cake pan, covering the upside down topping. Bake for 45 minutes or until a knife inserted comes out clean. Allow the cake to fully cool. Flip the pan upside down onto a large platter and peel the parchment paper off to reveal the cake. Serve and enjoy!