Step 1

Arrange a rack in the middle of the oven and heat to 400°F. Meanwhile, prepare the cake.

Step 2

Place the cauliflower florets and 1 teaspoon of the salt in a medium saucepan. Cover with water and simmer over medium-high heat until the florets are quite soft, about 15 minutes. They should break when pressed with a spoon. Drain and set aside in a colander to dry.

Step 3

Cut 4 round slices, each 1/4-inch, off one end of the onion and set aside. Dice the rest of the onion and place in a small frying pan with the oil and rosemary. Cook over medium heat, stirring occasionally, until soft, about 10 minutes. Remove from the heat and set aside to cool. Meanwhile, line the base and sides of a 9 1/2-inch springform pan with parchment paper. Brush the sides with melted butter, then mix together the sesame and other seeds and toss them around the inside of the pan so that they stick to the sides.

Step 4

Transfer the onion mixture to a large bowl. Add the eggs and basil and whisk well to combine. Add the cheese, flour, baking powder, turmeric, remaining 1 teaspoon salt, and plenty of pepper. Whisk until smooth. Add the cauliflower and stir gently, trying not to break up the florets.

Step 5

Pour the cauliflower mixture into the pan, spreading it evenly, and arrange the reserved onion rings on top. Bake until golden brown and set, about 45 minutes. A knife inserted into the center of the cake should come out clean. Let cool at least 20 minutes before slicing and serving. It needs to be served just warm, rather than hot, or at room temperature.