Season the salmon with salt and pepper on both sides. Make 2 or 3 slits across the skin of the salmon. Place a cast-iron skillet over high heat. Add enough peanut oil to lightly coat the bottom of the pan. Just as the oil begins to smoke add the salmon, skin-side down and cook for 4 minutes. Lower the heat and cook the salmon all the way on the same side, about 10 minutes - it will cook from the bottom up. During the last 30 seconds or so, spoon some of the oil over the top of the salmon to help cook it through.
While the salmon is cooking, make the sauce. In a stainless steel saute pan over medium heat, add 1 tablespoon butter and the oil. When the butter is melted, add the onions and cook until translucent but not browned, about 6 minutes, stirring constantly. Season with salt and pepper. Deglaze with the balsamic vinegar and red wine. Add the thyme and cook until the liquid is almost completely reduced, about 3 minutes. Add the cream and bring to a simmer. Cook until the cream is slightly reduced and starts to thicken, about 3 to 4 minutes, stirring occasionally. Be careful as the cream could boil over at this point. Once the cream is reduced, remove the thyme sprig. Season, to taste, with salt and pepper. Stir in the remaining butter.
Spoon the onion marmalade onto plates. Top with the salmon and garnish with chive flowers.