Heat your oven to 350°F (176°C). Line two 12 mold cupcake pan with 18 paper liners.

In a medium bowl, combine the flour, sugar, baking powder, baking soda and salt. Set aside. 

In another separate bowl, combine the streusel topping. Use a pastry cutter or two knives to cut the mixture into a course crumb texture. (A food processor works well also.)

In a separate large bowl, combine the melted butter, milk, vanilla, eggs and sour cream with an electric hand mixer. Add the dry flour mixture one spoonful at a time to the wet milk mixture until the batter is well combined. Do not over beat, this should take about 2 minutes. Stir in the chopped strawberries. 

Pour the batter into the prepared cupcake molds. Sprinkle the streusel topping on top of the muffins. Bake the muffins for 25 minutes until they are golden brown. Test with a toothpick to make sure they are fully baked.