Step 1: Preheat your oven to 375°F (190°C) and line a 12-cup muffin tin with paper liners or grease with non-stick spray.
Step 2: In a large bowl, whisk together the 2 cups of flour, granulated sugar, baking powder, 1 teaspoon of cinnamon, and salt.
Step 3: In a separate medium bowl, combine the melted butter, milk, egg, and vanilla extract until smooth.
Step 4: Gently fold the wet ingredients into the dry ingredients until just combined; be careful not to overmix the batter for your cinnamon pear muffins with walnut streusel.
Step 5: Fold in the diced pears until evenly distributed throughout the batter.
Step 6: Prepare the streusel by mixing the chopped walnuts, brown sugar, 2 tablespoons of flour, and 1/2 teaspoon of cinnamon in a small bowl. Cut in the cold butter using a fork or your fingers until the mixture resembles coarse crumbs.
Step 7: Scoop the batter into the prepared muffin tin, filling each cup about 3/4 full. Top each muffin generously with the walnut streusel mixture.
Step 8: Bake for 22-25 minutes, or until a toothpick inserted into the center of a muffin comes out clean.
Step 9: Allow the cinnamon pear muffins with walnut streusel to cool in the pan for 5 minutes before transferring to a wire rack to cool completely.