Bring a large pot of water to a boil. Mince the garlic, zest the lemon, measure 1 tablespoon lemon juice, chop the dill, and cut or tear the smoked salmon into bite-size strips.

Salt the boiling water and cook the pasta until about 1 minute shy of the package's al dente time. Before draining, reserve 1 cup of pasta water. The noodles should still have a slight bite because they will finish in the sauce.

Heat the olive oil in a 12-inch skillet over medium-low heat. Add the garlic and cook for 30 to 60 seconds, until fragrant but still pale. Add the heavy cream and lemon zest and bring to a gentle simmer. Stir in the Parmesan and cook for 2 to 3 minutes, until melted and the sauce lightly coats the back of a spoon.

Add the drained pasta to the skillet and toss over low heat, adding reserved pasta water a few tablespoons at a time until the sauce is glossy and clings to the noodles instead of pooling in the pan. Remove the skillet from the heat.

Fold in the smoked salmon, lemon juice, most of the dill, and the capers if using. Let the residual heat warm the salmon for 1 to 2 minutes. Taste before adding salt, then finish with black pepper and the remaining dill.