Preheat oven to 375°F. Butter eight 8-ounce ramekins and place on roasting pan. Set aside.
Cook pasta in salted water to al dente. Drain.
Return pot to stove and melt 1 tablespoon butter over medium heat. Add onion and stir to combine. Cook for a few minutes and then add garlic. Cook until garlic is fragrant and onion is softened. Slowly whisk in flour until a paste forms, about 30 seconds. Continue whisking for 1 to 2 minutes more. Slowly whisk in milk, cream, and 1 teaspoon salt. Increase heat to high and cook until mixture begins to thicken, about 10 minutes. Mixture should be thick enough to coat back of wooden spoon.
Reduce heat to low. Add shredded mozzarella, white cheddar, mild cheddar, and parmesan, and cook until the cheeses have melted and the sauce is smooth. Add cooked pasta, dried mustard and cayenne. Stir to incorporate. Divide mixture between prepared ramekins.
Melt remaining 3 tablespoons butter. Top macaroni and cheese mixture with bread cubes. Drizzle bread cubes lightly with melted butter.
In small bowl, combine garlic powder, onion powder, 1/8 teaspoon salt and pepper. Sprinkle seasoning mixture over buttered bread cubes. Top with cheddar cubes.
Place pan of ramekins in oven and bake minutes, or until the macaroni and cheese starts to bubble and the bread cubes start to brown. Place under broiler for about 5 minutes to crisp up the bread cubes. Remove from oven and let cool for 5 to 10 minutes before serving.