Preheat the oven to 350 and grease a muffin pan with some baking spray.
In a large mixing bowl, whisk egg, sugar, melted butter, sour cream, vanilla and milk.
Sift in flour, salt and baking powder. Whisk together until smooth.
Fold in cranberries and white chocolate chips.
Fill the muffin pan cups ¾ full with muffin batter and set aside.
In a medium bowl, combine brown sugar, white sugar and flour. Mix well until all ingredients are incorporated evenly.
Pour in melted butter and carefully fold it in with a large fork. You will want to be careful so you don't over-mix. Streusel should look like large crumbs and not paste.
Fold in minced, dried cranberries into streusel crumbs.
Sprinkle about two tablespoons of streusel on top of each muffin.
Bake for 27-30 minutes (Do a toothpick test to check if they are done. Tip: insert the toothpick in the batter part and try not to hit a cranberry).