Prep: 1. Bring butter to room temperature. 2. Preheat the oven to 350. Grease a small loaf pan. Set aside. 3. Zest and juice orange and separate 2 eggs. Make: 1. Mix the almond flour, gf flour, salt and the baking powder together in a bowl. Set aside. 2. Beat together the 2 yolks, 1 egg and milk. Set aside. 2. In a separate large bowl, cream the butter and the sugar together until light and fluffy. Gradually beat in the egg yolk mixture. Beat in the orange zest. Scrape sides as needed. 3. Using a spatula or wooden spoon, gradually fold in the flour mixture into the butter and eggs until well blended. 4. In a clean, dry bowl, with an electric mixer, beat the egg whites until foamy. Add cream of tartar and beat egg whites to soft peaks. 5. Gently fold the egg whites into batter, until well mixed. Pour the batter into the prepared loaf tin. 6. Bake for 45 minutes or until the cake is golden, and a toothpick comes out clean. Remove from oven and let the cake cool for 5 minutes, then carefully turn out the cake to cool on a wire rack. 7. Meanwhile, mix together the orange juice and sugar in a small saucepan. Heat gently over medium-low heat until the sugar has dissolved and syrup begins to thicken. 8. While the cake is still warm, spoon the syrup over it.
If you don't have cream of tartar on hand it's not strictly necessary, but it does really help the egg whites to get to the desired consistency. You can often find it in the bulk spice section, which is great since you'll need it for very little else. Room temperature egg whites, and a very clean, very dry bowl are also key to get the egg whites to the proper consistency.