Preheat the oven to 190'C.
Peel and dice the sweet potato into rough 2 centimetre cubes. Peel and crush the garlic using the back of a knife and a pinch of Maldon sea salt. Mix the garlic with the sweet potato, half of the olive oil and a good pinch of salt and pepper. Bake in the oven for approximately 20 minutes or until tender. Then remove from the oven and leave to cool.
Meanwhile wash and quarter the beetroot (you may need to cut it into eighths depending on the size). Add the remaining olive oil to a pan and fry the beetroot for a few minutes. When it begins to take on some colour add the thyme and allow to crackle away in the pan until fragrant. Then add the red wine vinegar and a glass of water.
Cook on a gentle simmer for 15-20 minutes or until tender. Then drain and leave to cool.
Flake the smoked mackerel and mix with the cooked sweet potato and beetroot. Finely chop the parsley and mix through along with the horseradish.
Season to taste and serve.
«A dish like this is great for garden parties in the summer as it can be made in advance and requires no last minute preparations when you are entertaining guests. »