Preheat oven to 375°F. Line a 12-cup muffin pan with paper liners. Make topping: Mix 1 1/4 cups all-purpose flour, 1/3 cup packed light brown sugar, 2 Tbsp. sugar, 1/2 tsp. cinnamon and 1 cup chopped walnuts. Add 8 Tbsp. melted unsalted butter; stir until moistened and clumpy. Set aside.
Make muffins: Mix 2 cups all-purpose flour, 2 tsp. baking powder and 1/2 tsp. salt. With an electric mixer on medium-high speed, cream 8 Tbsp. unsalted butter and 1 1/4 cups sugar until fluffy. Add 2 large eggs, one at a time, beating well after each. Lower mixer speed; add half of dry ingredients, then 1/2 cup milk and 1 tsp. vanilla extract. Stir in remaining dry ingredients. Fold in 1 cup chopped fresh cranberries.
Divide batter among muffin cups. Sprinkle topping over muffins, pressing lightly. Bake for 35 minutes, or until golden. Let cool in pan on a wire rack for 10 minutes, then remove from pan to rack