Bring orange juice and next 3 ingredients to a boil in a medium saucepan; boil over medium-high heat until reduced to about 1/2 cup. Reduce heat to low; whisk in butter, 1 piece at a time, until combined. Remove from heat; stir in chervil, salt, and pepper.
Dredge crabs in flour just until lightly coated. Heat 2 tablespoons oil in a large nonstick skillet over medium-high heat. When oil is hot, add half the crabs, top-side down; sauté 2 to 3 minutes per side, until golden, adding more oil, if needed. Drain crabs on paper towels, then transfer to a baking sheet in a 200° oven to keep warm. Repeat with remaining oil and crabs.
Serve crabs with asparagus and couscous; drizzle with the butter sauce.
"Did somebody say citrus-saffron? Sounds like a classic template for Sauvignon Blanc. Compared to light, lean versions from France, Artesa Sauvignon Blanc Reserve ($25), like many American versions, tends to have a bit more creaminess that pairs well with the rich sautéed crab. But it will also have plenty of the grape's characteristic herbalness-- a satisfying match with the asparagus, whose unusual taste often makes it a problem-child for wine." --Mark Oldman