HELPFUL TIPS: Vanilla isn't needed for this recipe (as some have suggested). Makes no difference ,and i put a heaping overflowing tsp. Neither my husband or friends can tell a difference, & I've made this 50+ times. Other than that, this recipe makes my husband a hero at his office! They say BETTER than any bakery! I use BROWN SUGAR instead of white for the topping. When I have buttermilk, i use that in place of milk. It's important to use butter at room temp (to a point that if you put a fork through it, it would smush). This makes it a lot easier to put on top. You can substitute blueberries with any fruit & it turns out great! Be sure to use PAM on the pan or they may stick. Also, frozen blueberries do not turn out the same. Fresh Fresh! Regular size tins make 12 at 18 min. Giant tins as recommended make 5-6 so double recipe! (Update 7/08): I noticed a lot of people had trouble w/their muffins sinking. You're over mixing or it's from adding TOO MUCH topping to 1 muffin using the given one. If you must drown yourself in topping, try this fail proof one I use that has less butter (perfect amount if doubling recipe): 2/3C brown sugar, 1/4C flour, 1/4 tsp cinnamon, 2T butter. Use fork to mix and has nice coarse texture. Just as crunchy & delicious w/the perfect muffin EXCEPT it doesn't cause the muffins to sink!