Whisk the all-purpose flour, whole-wheat flour, oats, cornmeal, brown sugar, baking powder and salt in a large bowl. Whisk the egg in a medium bowl. Add the yogurt, milk, lemon zest, nutmeg and oil and whisk until combined. Stir the egg mixture into the flour mixture until just combined (it's OK if there are a few lumps).
Heat a griddle or large nonstick skillet over medium-low heat; lightly brush with butter. Pour 1/4 cup batter onto the griddle for each pancake and cook until bubbles form on top and the bottom is lightly browned, about 3 minutes. (If the pancakes are browning too quickly, reduce the heat to low.) Flip and continue cooking until golden on the other side, about 1 more minute. Transfer to a plate. Repeat with the remaining batter, brushing the pan with more butter as necessary. Serve with butter and syrup.