First, cook the beetroots. If you’re using yellow and purple beetroot, cook them separately to avoid staining. Put in a large pan of cold water, bring to the boil and simmer until the beetroots feel tender in the centre when poked with a skewer – large ones will take about 40 mins, smaller ones about 20 mins. Leave in a colander in a sink until cool enough to handle, then peel off the skin plus any remaining stalky bits – rubber gloves will stop your fingers from staining!
For the croutons, heat oven to 200C/180C fan/gas 6. Trim the crusts off the bread and cut the bread into chunky croutons. Toss with the oil and poppy seeds to coat, plus a little salt, then spread on a baking sheet and bake for 8 mins until crispy. Leave to cool.
To make the dressing, lightly crush the blackberries with a fork. Whisk together the vinegar, oil, mustard powder and jam with some seasoning. Stir in the crushed blackberries, their juices, and the shallots.
To assemble, slice the cooked beetroots and arrange over 4 or 6 plates. In a large bowl, toss the leaves, croutons, blackberries and chives with some of the dressing, then crumble in the goat’s cheese and divide between the plates. Drizzle everything with a little more dressing, and serve.