Butter a 8x 8 baking dish as well as the sides of a 2 quart saucepan.
Pour the sugar, evaporated milk, milk, and salt into the sauce pan. Stirring frequently, bring to a boil over medium to medium-high heat.
Lower the temperature to medium or medium-low, then let continue to cook until it reaches 238 F.
Remove from heat and add the butter and vanilla. Resist the temptation to stir and instead let it cool to 110 F. This will take a good 20 to 30 minutes, but be patient, it's worth it.
Stir with a wooden spoon until the fudge thickens and loses it's sheen. Stir in the cereal, then transfer it to the buttered 8 x 8 dish.
Cover and let rest until hard, at least 4 hours, but overnight works just fine. Remove from pan and cut into pieces. Store in an air-tight container, or wrap individually in wax paper.