The "Berry-Best" Muffins
["1 c. butter", "2 c. sugar", "4 eggs", "2 tsp. vanilla", "4 c. flour", "1 c. milk", "4 tsp. baking powder", "1 tsp. salt", "4 to 5 1/2 c. fresh or frozen blueberries, blackberries, raspberries or cranberries"]
["If using frozen fruit, partially thaw and combine with 1/4 cup flour.", "Fresh berries should be rinsed, drained and well-dusted with flour before folding into batter."]
["butter", "sugar", "eggs", "vanilla", "flour", "milk", "baking powder", "salt", "blackberries"]