1 (6 ounce) box puffed rice cereal
2 cups granulated sugar
3/4 cup light corn syrup
1/2 cup water
1 teaspoon vanilla extract
Place puffed rice in a bowl. Combine remaining ingredients in saucepan and cook until mixture reaches soft-ball stage (see note). While stirring constantly, pour mixture over puffed rice. Continue to stir until cereal is completely coated. Grease hands with butter and roll mixture into balls when cool enough to handle. Cover with plastic wrap.
NOTE: Soft-ball stage means to heat the syrup to 234-240 degrees F. It is at this point that a small amount of syrup, when dropped into very cold water, forms a soft ball that flattens after it's removed.