On a work surface – wood or marble - make a well in the flour and add the eggs and tomato concentrate.

Gradually whisk the eggs and tomato concentrate into the flour.

Knead the dough for five minutes until it's smooth and elastic.

If the dough is too moist and sticky sprinkle in a bit of additional flour.

Cover the dough ball tightly with plastic wrap and let it rest for 30 minutes or more.

While the dough is resting prepare the filling.

Cut the the smoked salmon into tiny cubes, about ½ centimeter or ¼ inch.

Put the salmon in a mixing bowl and add the drained ricotta and grated Parmesan cheese.

Mix until fully blended, salt to taste and set aside.

Optional: gently toast the walnut halves in a saucepan just until golden.

Remove and set aside.

Break off the tough root ends of the asparagus and set aside for future use in a soup.

Cut off the asparagus tips, about 5-6 cm long pieces.

Cut the rest of the asparagus in half. You should have pieces that are about 5 to 6 cm (2 to 2 ⅓ inches) long.

Cut the asparagus pieces in half lengthwise (or in quarters depending on the thickness of the asparagus).

Cook the asparagus in a saucepan with a small amount of lightly salted boiling water + 2 tablespoons extra-virgin olive oil just until the asparagus are tender-crisp.

Use only enough water to cover the asparagus about halfway.

It should take no more than 3 to 5 minutes to cook.

Drain the asparagus and set aside, but reserve the asparagus cooking water.

Add the butter, lemon juice & lemon zest, the asparagus, and the freshly grated Parmesan cheese to the saucepan and cook on high for just 30 seconds.

You should have a thick, creamy sauce.

If necessary add some of the asparagus cooking water by the tablespoonful to the sauce but only if it's too dry.

Remove the asparagus tips from the sauce to set atop the ravioli when you serve.

Roll out the dough by hand or with a pasta machine until it's very thin.

The dough should be translucent.

Put about a teaspoon of filling along the pasta strips, spacing it about 3-4 cm or 1 ½ inches apart.

Cover with a second layer or strip of pasta and use your fingertips to gently seal the two strips of pasta together making sure to squeeze out any air bubbles.

Cut the ravioli by hand using a very thin sharp knife, or use a ravioli pasta tool to cut the individual ravioli.

Cook the ravioli in boiling salted water (the water should taste like the sea) until they are al dente, about 2 to 3 minutes.

The ravioli are very delicate so use a spider or a hand-held strainer to scoop them out of the pasta water.

Reserve the pasta cooking water.

Add immediately to the saucepan with the lemon-asparagus sauce and the freshly grated Parmesan cheese.

Gently toss to coat the ravioli with the sauce.

If need be add pasta cooking water to the sauce by the tablespoonful - just enough so that the sauce is creamy.