If using fresh egg pasta, roll it out very thin and cut it using the fettuccine/tagliatelle attachment of your pasta machine.

Trim and (if using fat asparagus, peel) your asparagus spears. Boil the asparagus in well-salted water until it is perfectly tender (not crisp-tender), about 5 minutes for thin asparagus, perhaps 7 for the thicker variety. (Test for doneness with a paring knife.) Cut off the tips and reserve, putting the tipless spears into a food processor with the heavy cream and a pinch of salt. Process until you have a perfectly smooth purée.

In a wide skillet, melt the butter. If using the shallots, sauté them gently for a minute or two. Add the asparagus purée and let it simmer for just a few minutes, until it has warmed and slightly reduced. Turn off the heat.

Now boil your pasta in well-salted water until al dente. For freshly made egg pasta, just drop it the boiling water and let it come back to the boil. If your pasta has been rolled really thin, that should be enough. If not, you can let it go for a minute or two longer, no more. If using store-bought tagliatelle, follow the instructions on the box.

While the pasta is cooking, sauté the asparagus tips with a nut of butter, just long enough for them to absorb the butter and warm up. Do not let them brown.

When done, drain and transfer the pasta to the skillet, along with a small ladleful of the pasta water, and mix it well with the asparagus purée over low heat. Let the pasta absorb the purée until it is well coated but slight quite slithery. You can add more water if things feel 'sticky'.

Serve with the sautéed tips on top, either in individual warmed plates or in a communal bowl for the table, with grated parmigiano on the side for those who like it.