Place the strawberries in a colander and rinse them under cold running water. Drain and hull the strawberries. Cut the larger berries in half or quarters and leave the small berries whole. Place the strawberries in a deep, heavy-bottomed pot such as Le Creuset and toss them with the sugar and Grand Marnier.
Bring the berry mixture to a boil over medium heat, stirring often. Add the apple and blueberries and contineu to keep the mixture at a rolling boil, stirring occasionally, until the jam reaches 220 degrees on a candy thermometer. This should take 23 to 35 minutes. Skim and discard any foam that rises to the top. Allow the mixture to cool to room temperature and then store covered in the refrigerator. It will keep refrigerated for at least 2 weeks. To keep the jam longer, pack and seal in canning jars according to the manufacturer's instructions.
Note: If you can't find
superfine sugar, you can use caster sugar
or pour granulated sugar into a food processor
fitted with the steel blade and process
until finely ground.