In a medium saucepan, add the mixed berries. Cook over medium heat, stirring occasionally until the berries begin to break down and release their juices (about 5-7 minutes).
Once the berries are softened, use a masher or fork to gently crush them to your desired consistency. For a smoother jam, you can also blend the mixture briefly with an immersion blender.
Stir in the honey or maple syrup, chia seeds, lemon juice, and a pinch of salt. Mix well to combine all the ingredients.
Reduce the heat to low and let the mixture simmer for another 5-10 minutes, stirring frequently. The chia seeds will absorb some of the liquid, thickening the jam as it cooks.
Once thickened and your desired texture is reached, remove from heat and allow the jam to cool to room temperature.
Transfer the jam to a clean glass jar or container and refrigerate for at least an hour to set further before serving.
Notes
Serve in a small jar with a sprig of mint on top, and pair with toasted bread or scones.