Heat oven: Preheat to 315°F (163°C). Grease and flour a loaf pan (or line with parchment).
Cream: Beat softened butter with sugar until light. Beat in maple syrup. Beat in eggs one at a time, then mix in vanilla, applesauce and greek yogurt until smooth.
Dry: Whisk whole wheat pastry flour, all purpose flour, almond meal, soluble corn fiber, lemon zest, salt and baking powder. Fold into wet mixture just until combined — do not overmix.
Bake: Spread batter in pan. Bake 70 minutes at 315°F until a toothpick in the center comes out clean and the top springs back. Tent with foil if browning too fast.
Cool: Rest in pan ~15-20 minutes, then turn out onto a rack to cool.