Put the oil, garlic, and shallots or onion in a large deep skillet over medium-high heat. Cook for just a minute or two, until the shallots or onion are softened and the garlic fragrant – you definitely don’t want to brown this. Crank the heat up to high, add the mussels and white wine, and cover the pan. Cook, giving the skillet a solid shake a few times, until the mussels open, 6 to 7 minutes. Set a strainer over a large bowl and pour the mussels into the strainer. Save that beautiful liquid for the chowder.
Melt the butter in a stockpot over medium-low heat. Add the onions, leeks, carrot, celery, and herb bouquet and season with salt and black pepper (be careful with the salt; the mussel liquid will be salty).
Cover and sweat the aromatics until they’ve softened, about 5 minutes. Take out the herb bouquet for a moment and stir in the flour and curry powder. Cook, stirring often, until four/roux smells toasty, about 5 minutes.
Stir in the stock and the liquid from the mussels and bring to a simmer. Drop the herb bouquet back into the pot and cook for 5 minutes. Add the potatoes, kick the heat up to medium-high, and bring back to a simmer. Cut the heat back and simmer until the potatoes are just tender, about 15 minutes.
Meanwhile, pull the mussels from their shells. Toss the shells into the trash, reserve the mussels, and add any liquid and aromatics to the chowder.
Bring the cream to a boil in a saucepan over medium-high heat. Boil for a minute or so to reduce the cream slightly, then turn off the heat. When the potatoes are tender, remove the herb bouquet. Stir in the mussels and cream, add the lemon juice, and taste for salt and pepper.
Ladle the chowder into wide soup plates, garnish with the lemon zest and chives, and serve. Serve this with big, flaky biscuits.