For the pickled beetroot, wash and trim the stems of beetroot. Put in a pan with cold water to cover. Bring to the boil, reduce the heat and simmer for 30 minutes until the beetroot is tender to the tip of a table knife.
Drain and leave to cool slightly. When cool enough to handle, rub off the skins with your fingers. Cut each beetroot in half.
For the pickling vinegar, put the sugar, vinegar, salt, mustard seeds, coriander seeds, black peppercorns and chilli flakes into a pan. Bring to the boil, stirring until the sugar dissolves, then remove from the heat.
Pack the beetroot into a large (500ml) sterilised jar then pour over the hot pickling vinegar. Seal with a vinegar-proof lid. Leave to stand for 2 weeks before eating.
For the beetroot salad, preheat the oven to 220C/200C Fan/Gas 7.
Lay a sheet of foil on a baking tray. Place the beetroots in the middle of the foil and cover with another sheet of foil. Crimp the edges all around to create a seal, leaving a 5cm/2in opening. Pour 4 tablespoons cold water into the opening, then seal tightly.
Transfer to the oven and cook for 1 hour. Remove from the oven and open the foil carefully to allow the steam to escape. Leave to cool slightly, then unwrap the packet. When cool enough to handle, rub off the skins with your fingers. Slice the beetroot and into a serving plate or bowl.
Mix the remaining ingredients together in a bowl, whisking until thoroughly combined. Pour over the dressing and season with salt and pepper.
For the roast beetroot, preheat the oven to 200C/180C Fan/Gas 6. Wash, trim and peel the beetroot, then cut into quarters.
Put the beetroot on a baking tray, pour over the olive oil, then sprinkle over the thyme leaves and season with salt and pepper. Add the garlic cloves in and toss everything to coat in the oil.
Roast for 40-50 minutes, or until tender, turning halfway through. Serve.