Preheat the oven to 400°. In a small saucepan of boiling water, blanch the zest for 1 minute; drain. Tie the cilantro stems and bay leaf into a bundle.
Melt 4 tablespoons of the butter in a large ovenproof skillet. Add the endives, cut side down, and season with salt and pepper. Add the juice, zest, cilantro bundle, coriander seeds and sugar and bring to a boil. Press a round of parchment on top, cover with a lid and braise in the oven for 30 minutes, or until very tender.
Transfer the endives to a platter. Strain the braising liquid into a glass measuring cup. In the same skillet, melt 1 tablespoon of butter. Add the endives, cut side down, and cook over moderately high heat until browned, 4 minutes. Turn the endives, add 1/2 cup of the braising liquid and cook, shaking the pan until the liquid is reduced to a glaze, 1 minute. Season with salt and pepper.
In each of 2 large skillets, melt 1 1/2 tablespoons of butter in 1 1/2 tablespoons of olive oil. Season the cod with salt and cayenne. Add 3 of the cod fillets to each skillet and cook over moderately high heat until browned and cooked through, 3 to 4 minutes per side. Set a piece of cod on each plate and arrange 2 endive halves alongside. Drizzle the remaining glaze over the fish and serve.
A full yet crisp and fruity Alsace Pinot Blanc with bitter notes will echo the rich, tart and bitter flavors here.