Prep: Preheat your oven to 330°F. Line a 12 cup muffin tin with nonstick muffin liners.
Combine ingredients separately: Whisk together all dry ingredients in a large bowl. In a separate measuring jug, whisk together all wet ingredients.
Make the batter: Pour the wet ingredients into the bowl with the dry ingredients. Fold just until combined, do not overmix. The batter will be quite thick.
Add to muffin pan: Evenly distribute the muffin batter between the prepared muffin cups (I find it works out the neatest if I do this with a large cookie scoop). Add streusel, if desired.
Bake the muffins: Bake in the preheated oven for 23-25 minutes, or until a toothpick inserted into the middle of a muffin comes out just clean.
The brown sugar is optional for a little sweeter and more decadent holiday treat. The muffins taste wonderful without it, too. (Nutrition facts are without sugar.)I added the topping on a whim when I made these for the blog, because they look a little plain on photos without it. Combine 3 tablespoons quick cooking oats, 1 tablespoon chopped walnuts or pecans and 1/2 teaspoon pumpkin pie spice in a medium bowl. Cut in 2-3 tablespoons stick butter and mix with your fingertips until small crumbs form. Sprinkle over the muffins just before baking, slightly pressing it into the batter to help it stick.