Grease a 10-inch springform pan, preferably nonstick, with butter and dust it with flour.
Preheat oven to 350°F.
Using an electric mixer, beat the egg yolks with the sugar to a smooth pale cream.
Beat in the citrus zests and almond extract.
Add the almond flour and mix well.
With clean beaters, beat the egg whites in a large bowl until stiff peaks form. Fold them into the egg and almond mixture (the mixture will be very thick; you will need to turn it over quite a bit to incorporate the egg whites).
Spoon the cake batter into the prepared pan, and bake for 40 minutes, or until it feels firm to the touch. Let cool before turning out.
Just before serving, dust the top of the cake with confectioners' sugar.