Preheat your oven to 200c. 

In the meantime. break up one medium Romanesco broccoli into florets and place in a pot of boiling water. Boil for just 5 minutes, drain and set aside.

Next, make your béchamel sauce (or for ease of use, I find the Italian store-bought pre-made ones excellent):

Warm up 250ml (1 cup) milk. Set aside. In a small saucepan over medium heat melt 1 tbsp butter, then add 1 tbsp flour and whisk or mix with a wooden spoon till the mixture starts to bubble a bit. Slowly whisk or stir in the milk, ensuring no lumps form. Once all the milk has been incorporated continue stirring until the milk has thickened considerably. Remove from the heat and incorporate 1 tsp Sriracha (or similar) and ½ cup grated Gruyère cheese.

Season with sea salt and pepper.

Place the broccoli in a baking dish, pour over the béchamel sauce and sprinkle with a bit more grated cheese.

Bake until bubbly, around 20 minutes.