Bring a large pot of generously salted water to a boil. Add the cauliflower florets and cook until crisp-tender, about 1 minute. This brief cooking time is crucial - you want the cauliflower to maintain some bite since it will continue cooking under the broiler. Drain immediately and set aside.

Base In a large skillet over medium-high heat, melt the butter. When the foaming subsides, add the finely chopped onion and season generously with salt and pepper. Sauté, stirring occasionally, until the onions become translucent, about 5 minutes. This step creates the aromatic foundation for your cheese sauce.

Add the milk and cream cheese pieces to the skillet. Cook, stirring constantly, until the cream cheese is completely melted and smooth. Decrease the heat to low and gradually add the cheddar, gruyere, Dijon mustard, grated garlic, cayenne, and nutmeg. Cook on low heat until everything is melted and combined, stirring frequently to prevent scorching.

Your sauce and season with salt and pepper. This is your chance to adjust the spice level - add more cayenne for heat or extra nutmeg for warmth. The sauce should be creamy, smooth, and well-seasoned.

Add the cooked cauliflower to the cheese sauce and fold gently to coat every piece. Transfer the mixture to a broiler-safe dish and broil until deeply golden and bubbling, about 2-3 minutes. Watch carefully during this step to prevent burning.

Remove from the broiler and immediately garnish with the toasted almonds and fresh chives. The almonds add a delightful crunch that mimics breadcrumb topping, while the chives provide a fresh, oniony bite that brightens the rich dish.