Peel and finely chop the onion. Peel and grate or finely chop the garlic. Finely chop the parsley stalks (keep the leaves for later). Thickly slice the chestnut mushrooms.
Melt half the butter over a medium heat in a large pan. Slide in the garlic, onion and parsley stalks with a pinch of salt and pepper. Fry for 5 mins, stirring, to soften.
Stir in the chestnut mushrooms and cook for 3-4 mins, stirring occasionally, till they look glossy.
Pour the pearl barley into the pan and add 300ml boiling water. Crumble in the stock cube and stir to dissolve. Bring to the boil, then reduce the heat to a simmer. Cover the pan with a lid (no lid? A large baking tray will do the job) and simmer for 10 mins. This is your orzotto.
While the orzotto simmers, pull the silks and leaves off the sweetcorn. Slice a sliver off the base so it sits upright on your chopping board. Run a knife down the cob to slice off the sweetcorn kernels. When the barley has cooked for 10 mins, stir the corn in and continue to cook, with the lid still on, for 10-15 mins.
While the barley cooks, thickly slice the portobello mushrooms and chop the sage leaves.
Bring 1 tbsp olive oil to a medium-high heat in a frying pan. Dust a little salt and pepper over the pigeon breasts and lay them in the hot pan. Cook for 5-6 mins, turning halfway, till golden. Transfer the pigeon breasts to a warm plate and leave to rest. Return the pan to the heat.
Add the sliced portobello mushrooms to the empty frying pan. Fry for 3-4 mins, stirring occasionally. Stir in the sage leaves and fry for a further min.
Roughly chop the parsley leaves and stir them through the barley along with the remaining butter. Taste and add more salt and pepper if you think it needs it. Spoon into bowls and top with the pigeon breasts, fried mushrooms and sage.