Preheat the oven to 375 degrees F—grease or line 12 cups of a muffin tin with paper liners.

Toss the fresh cranberries in the extra tablespoon of flour in a small bowl.

Make the walnut crumble: Combine the crushed walnuts, flour, sugar, ground cinnamon, and salt in a small bowl. Rub the softened butter into the dry ingredients with your fingers until a crumb forms. Set the crumble aside.

Make the muffin batter: Mix the flour, light brown sugar, ground cinnamon, baking powder, and salt in a large bowl until combined.

Whisk the eggs, buttermilk, and vanilla extract in a medium bowl. Pour the wet mixture and {cooled} melted butter into the dry mixture. Mix the ingredients until combined and a batter forms—do not over-mix. Fold in the chopped walnuts and fresh cranberries.

Spoon the muffin batter between the 12 prepared muffin cups. Evenly sprinkle the walnut crumble over the top of the muffins. Chill the muffins in the refrigerator for 10-15 minutes before baking.

Bake the muffins at 375 F for 20-25 minutes or until a toothpick inserted into the center of a muffin comes out clean.

Let the muffins cool in the muffin pan for 5-7 minutes before transferring them to a wire rack to cool completely.