1. Preheat oven to 375°. Prepare pasta according to package directions, stirring in asparagus and peas during last 2 minutes of pasta cooking time; drain.
2. Melt 4 tablespoons butter in a large saucepan over medium heat. Whisk in flour; cook 1 minute. Pour in milk; bring to a boil over medium-high heat, whisking constantly. Reduce heat to medium-low, and simmer 3 minutes or until sauce is smooth and thickened. Remove from heat; whisk in black pepper, cheeses, and 1/4 teaspoon salt.
3. Toss pasta with cheese sauce, vegetables, crab, and prosciutto. Spoon mixture into 6 (2-cup) greased ramekins, or a greased 13- by 9-inch baking dish.
4. Melt remaining 2 tablespoons butter in a saucepan over medium heat; add garlic, and cook 1 minute. Stir in panko and remaining 1/4 teaspoon salt, tossing to coat. Sprinkle evenly over pasta mixture. Bake 40 minutes or until topping is crisp and sauce bubbles. Let stand 5 minutes before serving.