Blueberry lemon jam: add blueberries, sugar, and lemon juice to a small saucepan over medium heat. Stir everything together and cook for about 20 to 25 minutes, stirring often, until the jam has thickened.

Remove the jam to a sealed container or jar and store in the fridge until time to use. 

Blueberry lemon mascarpone: in a small bowl, combine mascarpone, blueberry lemon jam, and lemon zest. Stir until combined fully.

Serve on toast or a bagel. Store in the fridge for up to a month.