First, you'll put your three sweeteners, peanut butter, salt, and milk in a heavy-bottomed pan.
Put the butter and the vanilla in the bowl of your stand mixer.
Stir over medium heat until the all the peanut butter has melted into the mixture. Bring to a boil. Keep stirring and cooking over medium-low heat until it reaches 234F.
Note that the video shows a double batch. That takes a bit longer to cook, so the color will darken a bit more than if you make a single batch. That's why it's important to keep stirring.
Once cool, beat the fudge on speed 3 of a Kitchen Aid (or on medium low with a hand mixer) until the candy is very thick, matte, and holds its shape on the beaters, about 5 min for a double batch.
Scrape the finished candy into your prepared pan and spread it out until even. If you like, you can scatter peanuts and finishing salt on top, pressing them down so they stick.
If using whole peanuts on top, slice through them with a serrated knife using a gentle sawing motion. One batch makes 64 small pieces of fudge. A double batch makes 64 large pieces!