If making your own fresh egg pasta: preparing the dough following the instructions in this post, then roll it out very thin (setting 3 on my KitchenAid attachment) and cut it into strips about 6mm (1/4 inch) wide using the fettuccine/tagliatelle cutter 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 5-6 minutes for thin asparagus, 7-8 for the thicker variety. (Test for doneness with a paring knife.)  Drain, refresh under cold water and pat dry.

Cut off the tips of your cooked asparagus and set them aside. Cut the rest into lengths and place into a food processor or blender 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.

Sauté the asparagus tips with a nut of butter and a pinch of salt, just long enough for them to absorb the butter and warm up. Do not let them brown. Add to the asparagus cream, reserving a few for garnish.

Boil your pasta in well salted water ntil al dente. (For extra flavor, use the same water you boiled the asparagus in, topped up if need be.)

For freshly made egg pasta, just let it come back to the boil. If your pasta has been rolled really thin, that should be enough. Otherwise, you can let it go for a minute or so, but no more. If using store-bought tagliatelle, follow the instructions on the box.

When the pasta is cooked, drain and transfer it to the skillet, along with a small ladleful of the pasta water.

Mix the pasta with the asparagus purée and tips 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.