Preheat oven to 350F. Line a muffin tin with paper liners.

In a medium bowl, mix together the flour, baking powder, spices, and salt.

In a large bowl, beat together the butter and brown sugar. Add the eggs, one at a time. Stir in the pumpkin puree and vanilla extract. Stir in the walnuts and raisins.

Add the dry ingredients to the wet ingredients, and stir just until incorporated; do not overmix.

Divide batter into 12 muffin cups and bake 20 minutes or until a toothpick inserted into one muffin comes out clean.

Let cool on a rack before serving.