1. Prepare the carrots:

• Begin by peeling the carrots and cutting them into julienne strips. If you’re new to julienne cutting, don’t worry! Simply slice the carrots into thin sticks about 2-3 inches long.

2. Cook the carrots:

• Place the julienne carrots into a medium saucepan and fill it with just enough water to cover them.
• Bring the water to a boil over medium heat. Once boiling, cover the pot and reduce the heat slightly. Let the carrots cook for about 6 minutes or until they are tender but not mushy.
• Beginner Tip: You can test the doneness by poking a carrot with a fork. It should go through easily but still offer some resistance. Overcooking will make them too soft to hold their shape in the casserole.
• Reserve ½ cup of the cooking water before draining the carrots. This starchy water adds flavor and helps bind the sauce.

3. Assemble the dish:

• Preheat your oven to 350°F (175°C).
• Transfer the cooked carrots to a 1½-quart baking dish, spreading them out evenly.

4. Prepare the sauce:

• In a medium bowl, combine the grated onion, mayonnaise, prepared horseradish, pepper, and the reserved carrot water. Stir until smooth and well-mixed.
• Pour the sauce evenly over the carrots in the baking dish, ensuring they are well-coated.

5. Make the breadcrumb topping:

• In a small bowl, mix the Panko breadcrumbs with the melted butter until the crumbs are evenly coated.
• Sprinkle the breadcrumb mixture over the carrots and sauce. This will create a golden, crunchy topping during baking.

6. Bake the casserole:

• Place the baking dish in the preheated oven and bake for 15 minutes, or until the breadcrumbs are golden brown and the sauce is bubbling.
• Beginner Tip: Keep an eye on the breadcrumbs in the final minutes to avoid burning. If they brown too quickly, cover the dish loosely with foil.