Coat an 8- x 8-inch square baking dish with non-stick cooking spray and set aside.
Coat the sides of a heavy medium saucepan with non-stick cooking spray. Add the sugar and evaporated milk and cook, stirring, over MEDIUM-HIGH until mixture boils. Boil for 1 minute. Remove from heat. Add crackers, peanut butter, and vanilla, stirring until peanut butter is melted. Let stand, without stirring, for 30 minutes.
Using a wooden spoon, beat vigorously until fudge becomes very thick and just starts to lose its gloss (about 4 to 5 minutes). Immediately spread fudge into prepared pan.
Melt chocolate chips in a double boiler or a small, heavy saucepan over MEDIUM-LOW heat, stirring often. Pour over fudge and spread out evenly with an offset spatula. Sprinkle with chopped peanuts.
Allow fudge to sit until chocolate has set and fudge is firm. Cut into 1-inch squares. Store in an airtight container.
Saltines need to be finely crushed which is easy to accomplish by pulsing in a food processor. Alternately, place them in a zippered plastic storage bag and use a rolling pin to roll over them.