Preparation

• In a small bowl, combine 2 Tbs. of the butter with the flour and set aside.
• Heat the remaining 1 Tbs. butter and the oil in a 5- to 6-quart pot over medium-high heat. Add the carrot and cook, stirring occasionally, for 2 minutes, then add the potato and leek and cook, stirring occasionally, until the leek begins to brown, another 5 minutes. Add the garlic and cook, stirring, until fragrant, about 30 seconds. Add the wine and cook until absorbed and evaporated, 7 to 10 minutes.
• Lower the heat to medium low. Add the stock, cream, bay leaf, thyme, 1/2 tsp. salt, and 1/4 tsp. pepper, and bring to a low simmer. Gradually add the flour-butter mixture, stirring after each addition, until slightly thickened, about 4 minutes. Add the cod and chopped dill, and simmer lightly until the cod is cooked through, about 5 minutes. Remove the bay leaf and thyme, season to taste with salt and pepper, and serve garnished with the dill sprigs and flaky sea salt.