Place the new potatoes in a medium to large saucepan, cover with water and bring to the boil over a high heat. Then reduce the heat to medium so that the potatoes simmer gently for 12–15 minutes, depending on their size. Test them with a fork to ensure they are definitely cooked through. Then drain them of all water and set aside to cool.
Simmer the asparagus in boiling water until just cooked, which should be about 2–4 minutes depending on the thickness of the asparagus. Drain and cut in half. Leave to cool.
To make the dressing, mix together the olive oil, balsamic vinegar and Dijon mustard, and season with a pinch of sea salt and some black pepper to taste.
Place the new potatoes and asparagus in a medium salad bowl, pour the dressing over and gently mix together well. Ready to serve.