Raspberry White Chocolate Chip Muffins

Streusel 2 tablespoons butter, softened 1/4 cup flour 1/4 cup brown sugar Muffins 1/2 cup butter, softened 1/2 cup sugar 1 egg 1/2 cup milk 1 1/4 cup flour 2 teaspoons baking powder 1 cup white chocolate chips 1 cup fresh raspberries