Bring 2 quarts water and 1 tablespoon salt to a boil in a large soup kettle. Add pasta and, using the time given on the package as a guide, cook, partially covered and stirring frequently at first to prevent sticking, until just tender. Add asparagus during last 5 minutes of cooking.
Meanwhile, microwave broth, evaporated milk, and garlic in a 1-quart Pyrex measuring cup or small microwave-safe bowl until steamy hot, 3 to 4 minutes; let stand for a couple of minutes.
Place butter in a Dutch oven or large saucepan over low heat. When butter melts, whisk in flour, then hot milk mixture all at once, whisking constantly until sauce thickens, 1 to 2 minutes. Stir in 1/4 cup Parmesan, salmon, lemon zest and dill. Add salt and pepper to taste and simmer to blend flavors, about 5 minutes. (Salmon will flake into bite-sized pieces as it cooks.)
Drain pasta, reserving 1 cup pasta cooking liquid. Return pasta to pot.
Pour cream sauce over pasta, adding enough reserve cooking liquid to moisten. Toss and serve immediately with a light sprinkling of Parmesan.
TIP: If you have any leftover pasta, pour it onto a baking sheet to cool quickly, then refrigerate. Save any remaining pasta cooking liquid to toss with pasta when reheating. (Leftover pasta can be refrigerated for up to 4 days. To reheat, microwave on high or warm over low heat, stirring in enough water or reserved pasta cooking liquid to make it creamy again.)
Recipe and image courtesy of Pam Anderson, author of The Perfect Recipe for Losing Weight & Eating Great (2008).