Place the salmon in a heavy saucepan or Dutch oven. Add the garlic, lemon peels, lemon slices, and enough olive oil to submerge. Season with salt.
Set the pan over the lowest possible heat and bring the oil to 170 F, monitoring it with a thermometer. Poach until the salmon is just opaque throughout but still slightly yielding in the center, about 10 minutes.
Lift the salmon carefully onto a rack-lined baking sheet.
Remove the lemon peels from the oil, finely slice them, and set them aside. Reserve 2 tablespoons of the poaching oil.
Position the oven rack at the highest position and set the broiler to high.
Broil the salmon 2 minutes until the surface is lightly golden in spots. The salmon should measure no more than 145 F in the thickest part.
Bring a large pot of heavily salted water to a boil. Add the pasta and lemon peels and cook till the pasta is just shy of al dente.
Remove the pasta and lemon peels and reserve 1 cup of pasta water.
Melt the butter in a wide skillet over medium heat.
Add the garlic and cook until soft, about 2 minutes.
Add the cream and lemon verbena, bring to a gentle simmer, stir in the marmalade, and reduce until slightly thickened, about 5 minutes.
Remove and discard the lemon verbena. Stir in 2 tablespoons of reserved poaching oil, lemon zest, lemon juice, and sliced poached lemon peels. Season with salt and white pepper.
Add the drained pasta. Add pasta water a splash at a time, until the sauce coats each strand. The lemon peels add more flavor and a confit texture, but they can be removed if you prefer a smoother texture.
Remove the pan from heat and fold in the ricotta gently, until partially combined but still slightly textured.
Divide the pasta among bowls. Set a salmon fillet on top. Finish with lemon zest and fresh lemon verbena leaves.