Preheat the oven to 350 degrees Fahrenheit. Finely dice the onion and thinly slice the garlic. Heat the olive oil in a small saucepan over a low/medium heat. Add the onion and garlic and sweat gently until tender.
Add the tomatoes, balsamic vinegar, and water. Bring to a gentle boil then reduce to a simmer. Simmer for 10-12 minutes until the tomatoes are soft and tender and the liquid has reduced right down.
While the tomatoes are simmering, place the brie in a small ovenproof dish. Alternatively, if your brie is pre-packaged in an oven-ready box, you may simply remove any plastic packaging and keep the brie in its box. Transfer to the oven and bake for 15 minutes. The cheese should be hot through and the center oozy and melted.
Once the tomatoes have finished cooking, let them cool a little, then add them to a food processor along with the onion, garlic, and a tablespoon of the cooking liquor. Blend to combine. You can blend to your preferred texture and leave the jam slightly chunky or process until smoother.
Add the pine nuts to a dry skillet over a low heat. Toast the pine nuts gently for 3-4 minutes or until lightly golden. Take care not to overcook as these will burn quickly.
Remove the hot cheese from the oven and top with the tomato jam and toasted pine nuts. Serve immediately to avoid the cheese firming. Serve with your favorite low carb dipping veggies or toasted Keto bread and crackers.