In medium-large size pot, combine the strawberries with the sugar and Cointreau and bring to a boil over medium-high heat. Stir often to prevent burning.
Add the apple and blueberries and keep the mixture at a boil, stirring often for about 30 minutes or until a candy thermometer reaches 220 degrees.
Using an immersion blender, gently blend the jam to give it an even texture. Skim any foam for the top and discard.
Transfer it to a container of your choice and store in the fridge for about 3 weeks. I also jar it in small batches and process the jars in boiling water using self sealing lids. This is an optional step but preserves the jam for much longer. I only recommend doing this if you understand canning.