Step 1

For the onions:

Step 2

Place all your ingredients in a pot and place it over high heat. Once the liquid comes up to a boil, bring it down to a simmer. Cook for 5 minutes. After 5 minutes, remove from the heat and allow the liquid to cool down to room temperature. After cooled down, remove the onions from the liquid and place it over a wire rack. Refrigerate the onions overnight.

Step 3

After refrigerating overnight, cut the root off the onion, exposing just enough where you can see all the layers. Remove the outer skin and the first layer. Then start with the center: Run your fingers around and carefully remove the middle layer. Move on to the next layer and repeat the process. Keep repeating until there's only 2 layers left and the onion is hollowed.

Step 4

Refrigerate the hollowed onions and reserve until ready to stuff.

Step 5

For the potato gratin:

Step 6

Pre-heat an oven to 350 F. Peel and slice your potatoes into a container of water.

Step 7

Strain all the water and add the potatoes, cream, salt and horseradish into a 2-inch-deep baking sheet. Make sure all the potatoes slices are evenly coasted. Triple-wrap with aluminum foil and bake for 45 minutes or until the potatoes are tender.

Step 8

Once the potatoes are tender and hot, fold in your Gruyere cheese. Mix well and cool down. Refrigerate until ready to stuff the onions.

Step 9

To assemble:

Step 10

When stuffing, add chunks of cold horseradish potato gratin at a time. Press the gratin well to remove any air bubbles taking care to make sure the outer layer does not rip. Repeat the stuffing technique until there's an even layer that meets the bottom.

Step 11

Pre-heat a convection oven to 450 F. In a nonstick oven-safe pan, place your onion in the middle, season with salt and black pepper and add the butter, olive oil and water. Roast for about 15 to 20 minutes or until the middle is hot. Baste every 5 to 7 minutes. When serving, baste one more time with butter, season gently with coarse salt and finish with finely minced chives.