Line the bottom of a 20-cm (8-inch) square pan with parchment paper, allowing the paper to hang over 2 sides for easy removal.
In a saucepan, combine all the ingredients except for the chocolate and vanilla extract. Bring to a boil and cook without stirring until a candy thermometer reads 111 °C (233 °F).
Immediately remove from the heat and let the temperature rise up to 112 °C (235 °F). Add the chocolate and vanilla without stirring.
Let cool for 5 minutes. Beat with a wooden spoon for 1 to 2 minutes until the mixture is very smooth (if you beat too much, the fudge will harden before you have time to pour it into the pan). Cool to room temperature. Cut into 25 squares.
Recipes with the "Healthy Pick" stamp have been evaluated by a registered dietitian member of the Ordre professionnel des diététistes du Québec.