Special equipment: a potato ricer
Preheat the oven to 400 degrees F.
Place the garlic on a square of aluminum foil and drizzle with 1/4 cup of the olive oil. Wrap the garlic tightly in the foil and bake until soft, 30 to 40 minutes. Unwrap the garlic and cool. Gently press the cloves between your thumb and forefinger to release the softened garlic into a small bowl. Set aside.
Add 2 inches of water to a large pot with a steamer insert. Bring to a boil then reduce to a simmer.
Add the potatoes to the basket, cover with a lid, and steam until easily pierced with a knife, about 20 minutes.
Add the cream, butter, 1 1/2 teaspoons salt and 1/2 teaspoon pepper to a small pot and heat until warmed; set aside.
Remove the potatoes from the steamer basket. Drain, and immediately press the potatoes and reserved roasted garlic through a potato ricer into a large bowl. Using a rubber spatula, fold in the cream mixture in batches until combined.
Preheat the oven to 250 degrees F. Line a baking sheet with parchment paper. Cut one lemon into 1/8-inch-thick slices, and juice the second lemon. Arrange the slices on the prepared baking sheet and place the thyme sprigs on top. Add the salmon fillets, skin-side down. Drizzle the lemon juice and remaining 2 teaspoons olive oil over the salmon, then sprinkle with the remaining 1/2 teaspoon salt and 1/2 teaspoon pepper. Place in the oven on the center rack and roast until the salmon is cooked almost all through at the thickest point, about 25 minutes. To check for doneness, make an incision with a sharp knife at the thickest point of a fillet and pull it apart to check for opaqueness; don¿t cook beyond medium-rare.
To serve, spoon some of the potato puree onto each plate, then gently place a fillet on top. Garnish with the lemon slices and the thyme sprigs, or just the leaves, and a dollop of caviar. Serve immediately.
Adapted from "Essential Emeril: Favorite Recipes and Hard-Won Wisdom from My Life in the Kitchen" by Emeril Lagasse. Oxmoor House Publisher, copyright MSLO, Inc., all rights reserved.