First make the pesto. Put all the ingredients in the small bowl of a food processor or blender and blitz/pulse to a rough chunky paste.
Heat the oil in a large sauté pan on a medium-high heat, then fry the shallots, celery, lemon rind pieces, chard stalks, a teaspoon of salt and a generous grinding of pepper for 10 minutes, stirring a few times, until it all starts to caramelise and soften.
Add the chard, cavolo nero leaves and asparagus, and fry, stirring, for two minutes longer, until the leaves wilt. Pour in the stock and peas, leave on the heat for two minutes or so, until boiling, then stir in the beans, cooked potatoes, tarragon and lemon juice, and divide between four bowls.
Spoon pesto on top, drizzle with a little more oil and serve hot. Garnish with more fresh tarragon and basil, if desired.