We tried this with the mass amounts of blackberries we have in our house. We wanted jam without dealing with fruit pectin, and this turned out way too sweet. I would recommend using more lemon juice/less sugar and also mashing the berries beforehand.
Here's a Gluten free, low carb recipe for Shepherds pie - its topped with mashed cauliflower. Its a nutrient dense meal in one. I kinda hate the idea of mashed cauliflower, but I do like shepherd's pie so I might do this sometime