2 cups brown sugar, packed
1 cup shelled walnuts
2 teaspoon ground cinnamon
3/4 cup softened butter, salted
3 large eggs
1 teaspoon vanilla extract
3 cups unbleached all purpose flour
1 1/2 cups sour cream
1 1/2 teaspoon baking soda
1 1/2 teaspoon baking powder
1/2 teaspoon salt
Preheat oven to 350°F.
Line muffin tins with paper liners or lightly grease with butter. Mince the walnuts until very fine, or grind in food chopper. In med bowl combine walnuts, 1/2 C brown sugar, and cinnamon, set aside. In large mixing bowl put remaining 1 1/2 C brown sugar, butter, eggs, and vanilla, using an electric hand mixer at med speed, combine until creamy-scraping bowl often.
Add flour, sour cream, baking soda, baking powder, and salt. Beat at low speed just until well mixed. Using a spatula fold and swirl in nut mixture until moist and incorporated throughout batter, but not completely blended, creating veins of nuts running through the batter.
Fill muffin cups 3/4 of the way to the top. Bake for 20 min or until muffin top springs back when touched. Remove muffins from tin immediately when done, cool on wire rack.