In a deep pot over low heat, place the milk with the brown sugar and the vanilla extract. Stir the mixture until it becomes incorporated and the sugar melts. Raise the heat and stir the mixture until it boils; then leave the mixture on the heat for about 3 minutes.
Take the pot off the heat and add the American Garden Chunky Peanut Butter. Stir the mixture until it is incorporated.
In a bowl, place the brown sugar, then add the peanut butter mixture, and then mix it using a hand or electric mixer for about 3-4 minutes. Pour the mixture in an oven sheet lined with parchment paper. Leave it aside at room temperature for about 2 hours until it cools.
Take the fudge out of the sheet after it cools; then cut it into cubes and serve.