6 pounds mustard greens, tough stems discarded and leaves torn
1 cup chicken stock
1/3 cup all-purpose flour
1/4 teaspoon cayenne pepper
Kosher salt and freshly ground black pepper
10 medium shallots, thinly sliced
Vegetable oil, for frying
1 1/4 cups heavy cream
1 garlic clove, smashed
Heat the olive oil in a pot. Add the onion and the crushed red pepper and cook over moderate heat, stirring, until translucent, 5 minutes. Add the greens in batches, stirring each batch to wilt before adding more. Add the stock and bring to a simmer. Cover and cook over moderately low heat until the greens are tender, 15 minutes. Drain the greens well and return them to the pot.
In a bowl, mix the flour with the cayenne and a generous pinch each of salt and pepper. Add the shallots and toss to coat with the flour mixture; transfer to a strainer and shake to remove the excess flour.
In a deep skillet, heat 1/2 inch of vegetable oil. Fry the shallots in batches over moderate heat until crisp, 2 minutes. Using a slotted spoon, transfer to paper towels to drain.
In a saucepan, simmer the cream and garlic over low heat until reduced to 1 cup, 10 minutes. Strain the cream over the greens and simmer over moderate heat until very thick, 5 minutes; season with salt and pepper. Stir in half the fried shallots and transfer to a serving dish. Sprinkle the remaining shallots on top and serve.
The stewed greens can be refrigerated overnight. The fried shallots can stand at room temperature for 4 hours.