- Line the bottom of a 20-cm (8-inch) square pan with parchment paper, letting the paper hang over two sides and butter the other two sides.
- In a heavy saucepan, bring all the ingredients except for the chocolate and vanilla to a boil, stirring to dissolve the sugar. Attach a candy thermometer in the centre of the pan and simmer without stirring until the thermometer reads 115 °C (240 °F). Remove from the heat and add the chocolate and vanilla without stirring.
- Place the pan in a cold water bath. Let cool without stirring, until the thermometer reads 43 °C (110 °F) or 20 to 30 minutes.
- Remove the pan from the water. With an electric mixer, beat until the mixture loses its gloss but is still soft, about 2 minutes.
- Pour immediately into the pan and spread with a spatula. Cover with plastic wrap and let cool for 1 hour at room temperature or 30 minutes in the refrigerator. Unmould and cut into 2.5-cm (1-inch) squares.
- Store in an airtight container. The squares of fudge can be made in advance and freeze very well.
White chocolate in your maple fudge? This is the secret to its creamy texture. It does not take much. A small 28 g (1 oz) square. That does not change the flavour of the fudge.