Melt the butter in a pan, then fry the spring onions for 1 minute, until softened. Add the wine and boil hard to reduce to about 2 tbsp. Stir in the crème fraîche, season well and add the nutmeg. Bring to the boil and simmer for 2-3 minutes until slightly thickened. Stir in the dill, if using, and squeeze in a little lemon juice. Set aside.
Blanch the shelled broad beans in boiling salted water for 2-3 minutes. Drain into a sieve and hold under running cold water to cool. Drain again and peel off the outer hard skin – make a nick in the tops and pop the beans out.
Trim the asparagus – if it’s young, it won’t need much cut off the stems. Cut into halves or thirds. Cook the pasta in salted boiling water as per pack instructions, adding the asparagus 3 minutes before the end of cooking time. Cook until “al dente”.
Drain well, reserving a little pasta water. Toss the hot pasta and asparagus with the drained broad beans, smoked salmon and sauce, loosening with a spoonful or two of pasta water, if necessary. The heat of the pasta should reheat the sauce and slightly cook the smoked salmon, but stir over a gentle heat to warm through if necessary. Serve immediately.