For hard-to-find spices, go to Kalustyans.com.
Sift together flour, cornmeal, baking powder, and cinnamon.
In a mixer bowl, beat together eggs, sugar, and vanilla on medium speed until doubled in volume. Reduce speed to low and slowly beat in oil, then white wine.
Fold flour mixture, Aleppo, and onion seeds into egg mix. Stir until just combined. Pour into greased baking pan and bake 1 hour.
Melt butter. When bread is done baking, remove from oven; prick 10 times with a skewer or toothpick. Pour butter over bread and let cool in pan. Cut into 3- to 4-inch-thick slices and serve.