Luscious lemon risotto

A couple of years ago I read Italian chef and food writer Anna del Conte's memoir, Risotto with Nettles. Nigella Lawson says del Conte was her mentor, and you can read Lawson's review of the book here.
       I photocopied some recipes, including a very intriguing one for Lemon Risotto, which del Conte says is one of her most popular dishes. I've been meaning to make it ever since, and this week, with two close friends coming to dinner - the kind you can experiment on and they won't mind if it goes wrong - I finally managed it. I was spurred on partly by my sister giving me some lovely shallots and garlic from her garden when I was in Auckland the week before.

Anna del Conte's risotto al limone
(Serves 4-6, depending on appetites)

60g unsalted butter
1 Tbsp extra virgin olive oil
2 shallots, chopped very finely
1 celery stick, chopped very finely
(you can chop these together by pulsing them carefully in the food processor)
300g risotto rice, such as Arborio or Carnaroli
1 litre light meat stock or vegetable stock
1 large lemon with unblemished skin
6 fresh sage leaves
small sprig of rosemary
1 free-range egg yolk
4 Tbsp freshly grated parmesan cheese, with more to serve if wished
4 Tbsp cream
sea salt and freshly ground black pepper

Heat 30g of the butter with the oil in a large heavy saucepan. Add the shallots and celery and cook gently until soft (about 7 minutes).
Mix in the rice and continue cooking gently, stirring, until the rice is well coated in the fats and partly translucent.

Heat the stock in a Pyrex measuring jug in the microwave or in another saucepan.
Pour about 150ml (roughly a sixth) into the rice. Stir thoroughly and cook, stirring regularly, until the rice has absorbed most of the stock.
Repeat, stopping halfway through to add the lemon rind and herbs (see below).

While the rice is cooking, zest the rind of the lemon, then squeeze out the juice and set it aside. Chop the herbs finely. Mix with the rind and stir into the rice when it has absorbed about half the stock..  

Continue adding stock and stirring until the rice is cooked but still a little al dente. (You may not need all the stock. Del Conte says good quality Italian rice takes about 20 minutes, but I find it takes a bit longer.) Take off the heat.
Call the eaters to the table and warm a dish or bowl for the risotto.
In a small bowl, combine the egg yolk, half the lemon juice, the parmesan, the cream, the remaining 30g of butter, and a very generous grinding of black pepper. Mix well with a fork. Stir this mixture into the risotto. Cover the pan and leave to rest for about 2 minutes. Taste for seasoning. (At this point I added the rest of the lemon juice, but suit yourself.)
Give it all an energetic stir, transfer to the hot dish or bowl and serve at once, with more grated parmesan alongside if you wish (I knew we would all wish, so it went on top).

This is a surprising and remarkably satisfying dish, because it combines subtlety and richness. I can't eat it as a first course, though - too filling. So I served it with a green salad and an artichoke-stuffed pork fillet from another Italian woman's book. But I'm writing in the intervals of making a great pot of minestrone for tonight, and it's getting to the stage where it needs my full attention, so I'll post that recipe next week.