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.
Spoon half the butter into a large pan and melt over a medium heat. Slide in the garlic, onion and parsley stalks before sprinkling in a little salt and pepper. Fry for 5 mins, stirring often, till softened.
Stir in the chestnut mushrooms and cook for 3-4 mins, stirring occasionally, till golden and glossy.
Pour the barley into the pan and add 300ml boiling water. Crumble in the stock cube and stir to combine. Bring to the boil, then reduce the heat to a simmer. Cover the pan with a lid (no lid? Just use a large baking tray) and simmer for 25 mins.
While the orzotto simmers, pull the silks and leaves off the corn cob. 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 10 mins left to cook, stir the corn in and continue to cook, with the lid still on, for the final 10 mins.
Slice the portobello mushrooms. Roughly chop the sage leaves.
Pour 1 tbsp oil into a frying pan and bring to a medium-high heat. Sprinkle a little salt and pepper on the pigeon breasts and lay them into the hot pan. Cook for 5-6 mins, turning halfway, till golden. Transfer the pigeon 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 1 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.