Place the carrots in a medium-size pot and just cover with water. Bring to a boil and let cook until fork-tender, about 20 minutes. Place the cooked carrots in a food processor with a few tablespoons of cooking water and about half a teaspoon of salt. Process until smooth and slowly add in 2 tablespoons of olive oil, with the motor running. Add more water if you want it to be smoother. Taste and adjust seasoning. (If you don’t have a food processor, use a food mill, blender, or an immersion blender.) MAKE AHEAD: You can make this the day before. Keep covered and chilled and reheat before serving.
Preheat the oven to 425 degrees F.
Cook the bacon in large frying pan over medium-high heat until beginning to brown, about 3 minutes. Add the Brussels sprout leaves and cook for 3 minutes or until bright green and beginning to wilt. Add the white wine and let simmer until it evaporates. Remove from heat and season the mixture with salt and pepper.
Season the cod with salt and pepper. Heat the remaining tablespoon of olive oil in a large, nonstick ovenproof skillet over medium-high heat until shimmering, and add the cod pieces (skin-side down). Sear the fish for 2 to 3 minutes on one side, or until a nice brown crust forms. Carefully flip the fish and place the pan in the oven. Cook for an additional 4 to 5 minutes or until the fish is opaque and flakes easily.
To serve: Place about half a cup of carrot puree in the center of each plate. Top with a piece of cod and spoon the Brussels sprout bacon mixture over each piece of fish. Serve immediately.