In a small saucepan, combine the blueberries, sugar and lemon juice. Stir occasionally over medium heat, until the blueberries start to soften and the mixture starts to bubble. Smash the blueberries with a potato masher or the back of a spoon. Let the mixture simmer gently until thickened to a jam consistency, about 2-3 minutes. Strain the cooked blueberries through a mesh sieve for a smooth consistency. You can skip this step if you prefer a chunky consistency. Set aside to cool to room temperature.