Melt the butter and chocolate in the top of a double boiler over simmering water, the upper pan should not touch the water.
Preheat oven to 325*F. Brush a 9 X 13 inch pan with melted butter and dust lightly with flour or spray generously with cooking spray.
Stir the flour, baking powder and salt together. In a medium bowl whisk together the eggs, sugar and orange zest until well blended. Add the orange and vanilla extracts to the melted butter ahd chocolate and stir into the egg mixture. Add the dry ingredients, mixing well. Spread the batter into prepared pan and bake 25 to 30 minutes until mixture is set, but not dry. Cool about 10 minutes.
Sift the sugar, flour and baking powder for the orange layer together in a large bowl. Whisk in the orange zest, orange and lemon juices, the orange flower water if using, and the orange extract. Whisk in the eggs, stirring until smooth. Pour over the pre-baked bottom and bake another 40 to 50 minutes, until the filling puffs up. The top should be light golden brown and the filling set. Cool completely. Refrigerate until cold before cutting. You will need to wipe the knife between cuts, as necessary -- to serve dust with confectioner's sugar if desire.