In a seperate bowl sift together flour, baking powder, baking soda, and salt.
Add to wet mixture in small batches.
Mix until combined.
Stir in walnuts.
Spoon into prepared muffin pan. Use muffin cups or grease and flour pan.
Fill muffin cups ⅔ full.
For topping.
Combine walnuts, flour, sugar, and cinnamon. Cut in butter until mixture crumbles.
Add topping mixture to tops of muffin batter.
Bake muffins for 20 minutes or until a toothpick inserted into the center of a muffin comes out clean.
Notes
If you fill the muffin cups ⅔ full you would get about 16 muffins. I don't like to use more than one pan (more to clean!) so I fill the cups up and get 12 muffins.