Preheat oven to 375F.
Place eggs, egg yolks, and mapel syrup in top of double boiler. Place over hot water and beat with an electric mixer only until foamy; do not cook. Remove from heat.
Heat milk with butter and pour half of it into egg mixture; reserve other half.
Beat mixture in double boiler on low until thickened but not to the point of a custard-like consistency.
Sift the flour. Sift again with the arrowroot, salt, and baking powder.
Pour egg mixture slowly into the flour mixture while stirring constantly. Add remaining milk-butter mixture and vanilla. Pour into two 9"x5" loaf pans lined with wax paper in the bottom. Butter the paper and sides of pans.
Bake at 375F for 30 to 35 minutes or until a toothpick comes out clean.
Cool on wire racks. Serve with whipped cream, fruit, or vanilla ice cream, as desired.
