Heat the oven to 200C (180C fan)/390F/gas 6.
Put the orzo and stock in a medium roasting tin, and top with the spinach.
Mix the mushrooms, two tablespoons of olive oil, the garlic and a teaspoon of sea salt in a bowl, then scatter all over the spinach. Put the tin in the oven and bake for 25 minutes.
When there’s 10 minutes of cooking time to go, put the hazelnuts, butter, the remaining tablespoon of oil and the sage in a small baking tray, scatter over a pinch of sea salt, then put on another shelf of the oven.
Once the orzo has had its 25 minutes, take it out of the oven and stir in three-quarters of the parmesan and the lemon juice and zest; you’ll probably also need to add a splash of boiling water or stock (just 50ml at a time) to get the mix to a nice, risotto-like texture – test by putting a spoonful on a plate: there should be some movement, rather than an orzo mountain.
Taste and add more salt or lemon juice as needed, then ladle into two warmed bowls.
Top with the hazelnuts, crisp sage and brown butter, scatter over the remaining parmesan and serve hot.
