1. Make crepe batter: In a blender, pulse flour, 1 Tbsp. sugar and salt. Add eggs and milk; blend until mixture is thick and no lumps remain. Pour into a bowl and let stand at room temperature for 30 minutes.
2. Make filling: Melt butter in a skillet; add apples. Sauté, stirring occasionally, until apples begin to soften, about 3 minutes. Sprinkle with remaining 3 Tbsp. sugar and cinnamon and sauté until apples begin to brown, about 5 minutes longer. Pour in juice; cook 2 minutes longer, stirring. Remove from heat.
3. Whisk batter. If necessary, thin with an additional tablespoon of milk (batter should have consistency of thin cream). Mist a 10-inch nonstick skillet with cooking spray and warm over medium heat. When pan is hot, ladle in 1/4 cup of batter. Quickly tilt skillet so batter coats surface in a thin layer. Cook until edges begin to brown, about 2 minutes. Lift edge of crepe and, using your fingers, carefully flip. Cook for 30 seconds; transfer to a plate. Cover with a clean kitchen towel. Repeat with remaining batter, misting skillet with cooking spray between crepes as necessary.
4. Over low heat, rewarm apple mixture. Fold each crepe into quarters. Arrange 2 on each plate and top with a portion of apple mixture and a dollop of yogurt, if desired.