Preheat oven to 200 degrees celsius. On a tray, scatter the sausages and potatoes. Dollop over 1 Tbsp of bone marrow cooking blend, season, and bake in the oven for 15 – 20 minutes. Remove the sausages and set aside, then return the potatoes to the oven for a further 5-10 minutes.
Cut the sausages into slices, and place in a large bowl with the potatoes and spinach. In a small bowl, whisk together the mayonnaise, spring onion, lemon juice, mustard and seasoning. Pour over the potatoes and toss to coat.