Preheat oven to 375 degrees F. Prepare a muffin pan, by spraying with cooking spray or lining with paper liners. Set aside. 

In a bowl, combine the dry ingredients (all-purpose flour, whole wheat flour, salt,  baking powder, cinnamon, and the lemon zest). Mix the dry ingredients together with a fork until combined. Set aside.

Using a stand mixer, cream together the butter and sugar until light and fluffy. Add the eggs and vanilla extract, mixing between. 

Gradually add one-third of the dry ingredients and then the milk, alternating between the two until all ingredients are fully incorporated. DO NOT OVER-MIX!

Using a spatula, gently fold the cranberries into the muffin batter. 

Spoon muffin batter into prepared muffin pan, filling each 2/3 full. 

Working quickly, add the Walnut Crumb Topping ingredients (except the butter) to a small bowl. Using a fork, stir the dry ingredients until combined. With the fork, "cut" the butter into the dry ingredients. (Mash the butter into the dry ingredients until the butter is in pea-sized pieces and evenly dispersed.)

Top each muffin with a spoonful of Walnut Crumb Topping. Gently press the topping down into the muffin batter so it doesn't spill right off. 

Bake muffins at 375 degrees F until golden and muffins spring back to the touch. (A toothpick will come out clean :) ) Enjoy!