Put the sugar and water in the saucepan and turn on the heat to high. Let the sugar melt without stirring. When the sugar becomes lightly colored, tilt the pan in different directions to keep the sugar moving.
When the sugar darkens to the color of bitter chocolate, put in the pine nuts and stir with a wooden spoon. At first lumps will form because the cold pine nuts cause the sugar to congeal, but as you stir you will see that the sugar liquefies again. Continue stirring until the pine nuts are evenly distributed and any lumps have dissolved. Pour over the aluminum-lined baking sheet.
Cut the potato in half at its narrower part. Discard one half. From the other half pare away about ½inch of peel close to the cut. Use the flat, cut side as a trowel to spread the sugar and pine nuts thinly and evenly over the aluminum foil.
When cold, peel away the croccante from the foil and break into irregular bite-size or larger pieces. Serve after dinner, or at any time as candy.