1. Combine sugar, milk, butter, and salt in a pan on the stove top.
2. Bring to a full rolling boil over high heat, stirring constantly.
3. Once it comes to the rolling boil, reduce to medium heat and stir constantly for approximately 5 minutes. Your candy thermometer should read 238 degrees which is the soft ball stage. ***This is very important***.
4. Remove from heat, stir in peanut butter.
5. Add marshmallow creme and vanilla.
6. Stir until well blended.
7. Optional - if you want to add M & M's, this is the time.
8. Spread in a 9 X 13-inch baking pan.
9. Cool.
10. Cut.
11. **Cooking time does not include cooling time.