Preheat the oven to 350°F. Prepare the pan(s) you are using by generously greasing them (if gluten is not an issue, baking spray works well). To make 24 mini cakes, use a mini muffin pan like this one on Amazon. For an 8-inch cake pan (like this one on Amazon), line the bottom with parchment for easy unmolding after greasing. Set the pan(s) aside for later.
Place the two oranges in a large saucepan, cover with cold water, and bring it to a boil. Boil the whole oranges for 20 to 30 minutes or until the skin feels softened and the fruit is beginning to collapse slightly.
Drain the oranges and refresh them under cold water to quickly cool them.
Coarsely chop the oranges and remove any seeds. Place the chopped orange in a mini food processor and process them until they become a paste and there are no more chunks. Set them aside.
In the bowl of an electric mixer fitted with the paddle attachment, beat the eggs and sugar on medium-high speed until they are thick and cream colored.
With a spatula, fold the ground almonds, baking powder and the orange paste into the mixture. Continue folding until all the ingredients are incorporated. Fill the prepared pan(s) with the cake batter and bake until a cake tester poked in the centre comes out clean. Be sure to bake until the edges are a dark golden. A 8-inch cake will take about an hour while smaller muffins take 30–40 minutes.
Let the pans cool 15 minutes on a rack before carefully unmolding the cakes.
To make the orange syrup
Zest the washed orange with a fancy zester (for nice ribbons of zest) or a microplane (for finer zest). Make sure to only take the outer layer of the rind and none of the white pith, which is more bitter.
Place the orange zest in a small saucepan. Add the sugar and the juice of the zested orange to the saucepan.
Bring to a boil, add a couple splashes of orange liqueur and simmer for 3 minutes or until the sauce is thickened.
To serve, drizzle the sauce over the cake.
This recipe makes 24 mini cakes (baked in mini muffin pans like these on Amazon) or one 8-inch cake (baked in a tall 8-inch cake pan like this one on Amazon)