In a medium bowl, whisk together quinoa, flour, baking powder, and salt. In another medium bowl, whisk together egg, egg white, butter, milk, and syrup until smooth. Add egg mixture to flour mixture and whisk to combine.
Lightly coat a large nonstick skillet or griddle with butter and heat over medium-high. Drop batter by heaping tablespoonfuls into skillet. Cook until bubbles appear on top, 2 minutes. Flip cakes and cook until golden brown on underside, 2 minutes. Wipe skillet clean and repeat with more melted butter and remaining batter (reduce heat to medium, if overbrowning). Serve with maple syrup and fresh fruit or preserves, if desired.