Preheat oven to 350°. Place liners into muffin tin and spray with non stick spray.
In a large mixing bowl, add flour, brown sugar, baking powder, cinnamon and salt and mix together with a spoon.
In a small bowl, beat the eggs, then add the sour cream, vegetable oil and vanilla extract.
Add the egg mixture to the dry mixture and combine but do not over mix.
Spoon muffin mix into liners two-thirds full.
In a medium bowl, mix the granulated sugar, brown sugar, cinnamon, salt, flour and walnuts together. Pour the butter over the mixture and mix. It should form a crumbly mixture.
Place a couple of spoons of crumb topping on the tops of each muffin. Press down slightly. Add topping evenly till it is all used.
Place muffins in the oven and bake for 25 minutes. Insert a toothpick into the middle. If it comes out clean, they are done. If it doesn’t come out clean, you may need to bake for an additional 5 minutes.
While muffins are baking, make the glaze. In a small bowl mix confectioners sugar, vanilla and milk together. Should be runny consistency.
Remove muffins from the oven and allow to cool for 10 minutes. When cooled, pour icing over the tops.