Preheat oven to 375°F (190°C) and set the rack to the middle.

Pour 1/2 cup of water into a pot fitted with a vegetable steamer.

Cover the pot and set over medium heat.

Once the water boils, add cauliflower florets to the steamer.

Cover and steam until tender but not mushy, about 10 minutes.

Remove from heat.

Grease the bottom and sides of a small casserole dish.

Arrange the steamed cauliflower florets in a single layer inside the dish.

Add butter to a small heavy saucepan and melt over low heat.

Add diced shallot and cook until gently browned, stirring occasionally, about 3 minutes.

Whisk in flour, white pepper, nutmeg, and cumin.

Continue to cook, stirring constantly, until pale golden brown, about 3 minutes.

Slowly whisk in milk and heavy cream and cook, stirring constantly, until the sauce comes to a boil and coats the back of a spoon.

Remove from heat and stir in 1/2 cup of the grated pecorino Romano cheese.

Season the sauce to taste with kosher salt.

Pour the sauce evenly over the cauliflower in the casserole dish.

In a small bowl, combine panko bread crumbs, melted butter, and remaining pecorino Romano cheese.

Stir well to combine.

Sprinkle the bread crumb mixture evenly over the top of the cauliflower florets.

Bake in the preheated oven until the topping is gently browned, about 20 minutes.

Sprinkle with chopped fresh parsley and serve immediately.

Alternatively, sprinkle with more cheese and broil briefly for a darker, crisper topping.