In a large bowl, combine flour, sugar, salt and baking powder. Set aside.
In a smaller bowl mix egg, oil, milk, sour cream and vanilla.
Make a well in the center of the dry ingredients and pour liquid ingredients into dry ingredients. Mix to incorporate, stopping before fully blended.
Gently fold in frozen fruit, mixing only to distribute fruit.
Scooping and Filling
Spray or grease muffin pans and rim of pan for overflow.
Using a scoop or measuring cup portion batter into muffin well. It should completely fill well.
Sprinkle tops of muffin batter with a generous sprinkle of sugar, about 1 tsp. each.
Baking
Place muffins in the center of preheated oven. Make sure there is room for these to bake tall.
Since all ovens bake differently, Set timer for 25 minutes and check for doneness. The best part of these muffins is their crusty tops so give them all the time they need.