Preheat oven to 200°C. Wrap the beetroot in foil and arrange on an oven tray, then bake for 1½ hours. Unwrap, then peel while still warm.
Bring the stock to a simmer in a large saucepan, then whisk in the semolina, simmering until thick but smooth. Fold in the cheeses.
Combine the seeds in a mortar and pound until crumbly, then mix with the walnuts and broccoli powder. Cook thepork sausages gently over a flat barbecue plate, turning regularly until firm to touch. Serve with the semolina, crumble and a drizzle of walnut oil.