Prepare an 8” x 8” pan by buttering it all over and then line it with parchment paper that hangs over two of the sides. Set aside.
In a medium saucepan, heat the whipping cream, brown sugar, granulated sugar, and the maple syrup on medium-low, stirring constantly with a wooden spoon. When the sugars have dissolved, stop stirring. Continue heating the mixture until it reaches 239ºF (115ºC), then take the pan off the heat.
Pour the nuts over the hot fudge mixture and let rest at room temperature for another 20 minutes to cool slightly (alternatively, you can set the pan in a shallow bowl of cold water for 10 minutes). You want the fudge temperature to drop to below 50ºC and this is best measured with a probe thermometer which takes faster readings than older candy thermometers.
Stir the fudge mixture for 3 minutes with a wooden spoon, until it becomes quite thick, opaque, light in colour, and has lost some of its shine. Quickly transfer the fudge mixture to the prepared 8” x 8” pan, pushing it into the corners and smoothing it out as fast as you can. Use the parchment overhang to press down and smooth the surface.
Let the fudge set for 1 hour minimum at room temperature before cutting it into small pieces.