Blanch the peas in boiling water for 3 minutes or steam over boiling water. Drain and rinse them with cold water. (Keep a small cupful of the cooking water).
Put the peas, rocket leaves, vinegar, garlic and oil in a food processor and whiz for a few seconds.
Cut the spring onions into thin slices, then add to the blender, together with the crumbled Stilton. Whiz again, until you get a textured paste. Leave it a bit lumpy - it shouldn't be too creamy.
Add a little cooking water, if you want it as a dip, more if you want it as a pasta sauce. You can whiz it a few more seconds.
Season with salt and pepper, then spoon it into a serving bowl.
Let it rest in the fridge for at least 30 minutes, or serve it immediately as a pasta sauce.