With the rack in the middle position, preheat the oven to 350°F (180°C). Line a baking sheet with a silicone mat or parchment paper. Butter and line an 8-inch (20 cm) square dish with parchment paper, letting the paper hang over two sides.
Scatter the peanuts on the baking sheet and roast for 12 minutes in the oven. Let cool.
Meanwhile, in a pot over medium-high heat, bring all the ingredients, except the peanuts, to a boil. Continue boiling without stirring until the mixture reaches 241°F (116°C). Remove from the heat and let rest for 30 minutes without stirring.
Add the peanuts. Using a spatula or wooden spoon, stir until the mixture thickens and lightens in colour, about 5 minutes. Quickly pour into the dish and smooth the surface. Let cool completely. Unmould and cut into 1-inch pieces. The fudge will keep for 2 weeks in an airtight container at room temperature.
Recipes with the "Healthy Pick" stamp have been evaluated by a registered dietitian member of the Ordre professionnel des diététistes du Québec.