In a large sauce pan, place oranges in their entirety with water to cover. Bring to a boil. Continue to boil for 2 hours, or until very very soft. Keep an eye to make sure that the oranges always have water to cover. Let cool.
While the oranges are cooking, prepare the pan or pans by taking the base of the springform pan and "tracing" it with the point of a knife onto parchment paper. Cut along the "line", and place onto the base of pan. Repeat if using multiple pans.
Spray parchment and walls of pan with cooking spray. Sprinkle base and walls with 3 Tablespoons of almond flour. Set aside until ready to use.
Preheat oven to 375℉.
While oranges are cooling, with an electric mixer, beat the eggs. Add extra fine sugar, remaining 1 cup of almond flour and baking powder. Mix thoroughly.
Once cool enough to handle, cut oranges in half. Carefully take out any seeds and discard.
Place 4 orange halves into the bowl of food processor or blender. Puree until smooth and of even consistency.
Add orange puree to the egg mixture. Mix thoroughly.
Pour mixture into prepared pan or pans. Bake for an hour, or until tester comes out clean. Let rest for about 20 minutes.
Gently loosen from pan and remove base and parchment circle. Allow to cool completely. Depending on which side you prefer as the good side, you may chose to invert onto serving plate or plates.