3 small unpeeled whole oranges (Valencia or blood oranges work best)
2 c. almond flour
1 1/2 c. sugar
1 tsp. baking powder
1/4 tsp. salt
5 eggs, separated
1 tbsp. freshly grated lemon zest
1 tsp. pure vanilla extract
-Put the oranges in a deep pot and add enough water to cover (the oranges will float, this is okay). Bring water to boil then lower to a simmer. Cook uncovered for 1 hour (replenishing the water as it evaporates).
-Drain oranges and set them aside until they're cool enough to handle. Cut each orange into eighths and remove the seeds.
-Separate the oranges into 2 equal batches - set one aside. Finely chop one batch of oranges, or place in a food processor. Set aside.
-Preheat oven to 375. Butter an 8" round springform pan and line the pan bottom with parchment paper. Set aside.
-In a medium bowl, mix the flour, 1/4 c. of the sugar, the baking powder and the salt. Set aside.
-In a large bowl, whisk the egg yolks with 1/2c. plus 2 tbsp. of the sugar until the eggs are thick and pale yellow in color. Stir in the lemon zest and vanilla. Continue to whisk for 5 minutes, or until thick. Fold in half of reserved oranges and then half of the dry ingredients. Repeat until all of the reserved oranges and dry ingredients are added in.
-In a new bowl, beat the egg whites until they hold soft peaks. Gradually add the remaining 2 tbsp. of sugar, beating until the whites are stiff but not dry. Fold the whites into the orange batter in 3 additions, blending completely each time.
-Pour the batter into the prepared pan and bake for 45-55 minutes on middle rack. (If the cake top browns too quickly cover with foil).
-Allow cake to cool completely.
*This cake can be made 1 day ahead. Store at room temperature, wrapped in foil.