Melt olive oil and marg/coconut together in large ovenproof dish at 190C. Add beetroot, syrup & vinegar. Season and stir. Cover with foil and bake at 190C for 30-40 min (to tender).
If making pastry: Mix flour with salt. Add fat. Add just enough water to bring together. On a floured surface, shape into a rectangle, roll to about 1cm thick and fold into thirds. Turn ΒΌ and repeat the rolling and folding five more times. Wrap and rest in fridge 30min.
When beetroot is cooked, arrange neatly in dish. Roll pastry larger than dish and place it over, tucking in any excess. Bake 20-25min to golden.
Shake together vinaigrette ingredients in jam jar.
Rest tart a few minutes after baking. Carefully and quickly turn over onto a plate. Pour over vinaigrette and serve.