This is not a cake at all in the traditional sense. It is more like a frittata than a cake, but it is not a frittata either. It is delicious whether you eat it just after you have made it or the next day. Once you have made the original cauliflower version feel free to riff on it. You can make it with other vegetables and it will still be good. I have not had the chance to do that myself but a friend of mine has done so with very good results. I have only made one change to Yotam Ottolenghi's recipe from his book Plenty More, I roasted the cauliflower rather than simmer it in water.
serves 4 to 6
1 small cauliflower, outer leaves removed and broken into small florets. About 4 cups.
1 medium red onion, peeled
5 tablespoons olive oil
1/2 tablespoon finely chopped fresh rosemary
7 large eggs
1/2 cup fresh basil leaves, chopped
1 cup sifted all-purpose flour
1 1/2 tsp baking powder
1/3 tsp ground turmeric
1 1/2 cups coarsely grated Parmesan cheese or other aged cheese, about 6 ounces or more if you are feeling generous. The original recipe calls for 220 grams which translates to almost 8 ounces
melted unsalted butter for brushing the pan
1 1/2 tablespoons sesame seeds (or 1 T sesame seeds and 1 tsp nigella seeds. I have never seen nigella seeds but that is what Ottolenghi calls for in his original recipe. They would be prettier.)
Salt and black pepper
Heat the oven to 425º. Line the base and sides of a 9 1/2" springform pan with parchment and brush with melted butter. Cover the sides with the sesame seeds.
Toss the cauliflower florets with some of the olive oil and some salt and roast until tender. Remove from oven and allow to cool. Turn the oven down to 400º.
Cut 4 slices from one end of the red onion and separate the rings. Chop the rest of the onion and sauté until soft in the rest of the oil with the rosemary. Let the onion cool. Meanwhile whisk together the eggs and basil, then whisk in the flour, baking powder, turmeric, Parmesan, 1 tsp salt, and plenty of pepper. When smooth, stir in the onion and cauliflower. Pour the cauliflower mixture into the pan and lay the onion rings on top. Bake in the center of the 400º oven for about 45 minutes, until the cake is golden brown and set. A knife inserted into the center of the cake should come out clean. When the cake is done allow it to cool for at least 20 minutes before serving. It is best not to serve it hot. When it is completely cooled you can wrap it and refrigerate to serve the next day.