Warm milk to room tempurature (30 seconds in the microwave). Add lemon juice to milk and let stand for 5 minutes. Whisk dry ingredients. Whisk egg whites, whisk into milk. Mix egg yolk into melted butter, then stir into milk. Dump wet ingredients into dry all at once. Whisk until just mixed.
Heat griddle over medium-high heat. When water splashed on the surface sizzles, pour batter in 1/4 cup at a time. Turn when the top starts to bubble. Cook for 1 more minute.