Preheat the oven and prepare the soufflé dish - Preheat your oven to 375 degrees Fahrenheit. Butter the inside of a 6-inch soufflé dish, starting from the bottom and working your way up. Dust the dish with parmesan cheese, coating the buttered interior. Set aside.

Make the roux paste - In a medium saucepan, melt butter over medium heat. Slowly whisk in all-purpose flour. Keep whisking until a thick paste forms, and the mixture begins to turn golden brown, about 3 minutes. - Be mindful of the heat, as the mixture can brown too quickly and burn. The roux paste should have smooth consistency, without lumps.

Add the milk and spices to the roux paste - Whisk in the whole milk, salt, black pepper, and nutmeg powder to the roux paste. Keep whisking until the mixture thickens and begins to bubble, about 5-7 minutes. Remove from heat.

Separate the eggs and beat the whites - Crack the eggs and separate the yolks from the whites. In a mixing bowl, beat the egg whites with an electric mixer until they form stiff peaks. - Make sure that there are no traces of yolk in the egg whites, as this can make them harder to beat. Also, make sure that your mixing bowl and beaters are completely clean and dry, as any trace of oil or moisture can also prevent the egg whites from stiffening.

Mix the egg yolks and soufflé mixture - Whisk the egg yolks into the soufflé mixture, making sure they are fully combined. Gently fold in the beaten egg whites, one-third at a time, making sure they are fully incorporated into the mixture. - Be gentle when folding in the egg whites, as you don't want to deflate the mixture and lose its fluffiness. Also, avoid overmixing, as this can make the soufflé less fluffy and may cause it to collapse during baking.

Layer the soufflé batter and grated cheese into the dish - Pour one-third of the soufflé mixture into the prepared soufflé dish. Sprinkle half the grated Gruyere cheese over the mixture, making sure it's evenly distributed. Pour another one-third of the soufflé mixture over the cheese layer. Add the remaining grated cheese on top. Finally, pour the remaining soufflé mixture over the cheese layer. - When layering the cheese and soufflé mixture, be careful not to mix the layers. Each layer should be distinct and separate from each other to ensure even cooking.

Bake the soufflé - Place the soufflé dish on a baking sheet and place it in the preheated oven. Bake for 35-45 minutes or until the soufflé is golden brown and puffy. Don't open the oven door for the first 30 minutes of baking to prevent the soufflé from collapsing. - Make sure the oven is fully preheated before placing the soufflé inside. Avoid opening the oven door during the first 30 minutes of baking to ensure that the soufflé rises properly. Check the soufflé frequently towards the end of the baking time, as it can brown and burn quickly.

Serve and enjoy - Remove the soufflé from the oven and place it on a cooling rack for 5 minutes to cool down. Garnish with chopped chives and serve immediately. - The soufflé is best served right away, as it can deflate and lose its fluffiness over time. Make sure to enjoy it while it's still warm and puffy.