Preheat an oven to 350°F. Grease 14 standard muffin cups with butter or nonstick cooking spray.
If you are making the topping, now is the time to, stir together the sugar, walnuts and cinnamon in a small bowl. Set aside.
To make the muffins, in a bowl, stir together the flour, sugar, cinnamon, nutmeg, baking powder, baking soda and salt.
In another bowl, whisk together the eggs, oil, buttermilk and vanilla until blended. Add the flour mixture, stirring just until evenly moistened. The batter will be slightly lumpy. Using a large silicone spatula, gently fold in the pears and walnuts just until evenly distributed, no more than a few strokes. When mixing, take care not to break up the fruit. Do not overmix.
Spoon the batter into the prepared muffin cups, filling them level with the rim. Sprinkle the muffins with the topping, dividing it evenly. Fill the unused muffin cups one-third full with water to prevent warping. Bake until the muffins are golden, dry and springy to the touch and a toothpick inserted into the center comes out clean, 20 to 25 minutes. Transfer the pan(s) to a wire rack and let cool for 5 minutes, then unmold the muffins onto the rack. Serve warm or at room temperature. Makes 14 muffins.