Mix all JIF peanut butter, salt, vanilla and 10x confectioner's sugar together in large bowl with electric mixer until well blended.
While mixing, melt the 3 sticks of butter in the microwave.
Add the melted butter to the sugar mix, and mix well and fast. It will be a sticky consistency. Dump into a 9x13 pan and using your hand - pat/smash across the bottom of the pan and smooth out top.
Put into refrigerator to cool. Ready to eat in 15+ minutes.
For smooth fudge, use smooth peanut butter. For nutty fudge, use chunky peanut butter. Decorate with sprinkles and press down into top for decorating, before refrigerating. I use sprinkles based on the holday - red/white/blue for 4th of July, green/red for Christmas, orange/black for Halloween, etc. I've also melted chocolate chips and poured over the cooled top, gives a Reese's peanut butter cup flavor!
NOTE: If you put foil in pan before fudge mixture, you can lift out on the counter and use a pizza cutter to cut this and it goes very fast. I only recommend JIF peanut butter and margarine, not butter. I've given this recipe out in the past and people have changed those ingredients and it doesn't come out the same.