- Heat oven to 350 °F.
- Grease 24 3-inch muffin pan cups or line with paper liners.
- In large bowl, combine flour, 1 cup sugar, the baking powder, salt, orange zest, and nutmeg.
- With pastry blender or fork, cut in ¾ cup (1½ sticks) butter until mixture is crumbly.
- In medium bowl combine apple, yogurt, and eggs; add to flour mixture, stirring until just combined.
- Spoon batter into prepared muffin cups and bake 20 to 25 minutes or until centers spring back when gently pressed.
- Cool muffins in pan 5 minutes; remove from pan and cool until able to handle.
- Meanwhile, melt remaining ½ stick butter.
- In small bowl, combine remaining ¾ cup sugar and the cinnamon.
- To serve.
- Brush tops of muffins with butter and roll top in cinnamon-sugar mixture.