Lightly butter a 8x8 pan.
Whisk together sugar, cocoa powder, salt and milk in a medium sauce pan.
Bring the cocoa milk mixture to a boil over medium heat. Stir constantly until the mixture reaches 245 degrees.
Remove from heat and stir in the Velveeta, peanut butter, butter, and vanilla.
Using a whisk, rubber spatula or spoon – stir or whip vigorously until the fudge thickens. Approximately 8 to 10 minutes.
Stir in nuts or other mix-ins.
Pour into prepared pan and tab gently on the counter to even out the fudge.
Allow to set at room temperature for several hours.
Cut using a thin blade, wiping blade clean between slices. I cut it into squares a little less than an inch in size.