Preheat the oven to 450ºF. Spray a 2-quart baking dish or 9 inch cast iron skillet with nonstick cooking spray.
Bring a medium pot of water to a boil. Add the cauliflower and cook until tender, 5-8 minutes. Drain well, then transfer to the baking dish.
Meanwhile, melt the butter in a medium saucepan over medium-low heat. Add the shallot and minced garlic. Cook until the shallot is softened, 2 minutes. Whisk in the flour; whisk for 3 minutes. Add the milk in a slowly, whisking constantly. Bring the mixture to a boil. Reduce the heat to a simmer, whisking occasionally, until the mixtures slightly thickens, about 5 minutes. Remove from the heat and add half of the gouda, salt and pepper. Stir until the cheese is melted. Then add the other half of cheese. Whisk until sauce is smooth. Pour the cheese sauce over the cauliflower and stir gently to combine.
Combine the panko breadcrumbs and the parmesan cheese. Sprinkle evenly over the top and bake until the topping is golden brown, about 10 minutes.
