Bring a large saucepan of water to the boil with 1/2 tsp salt.
Halve, peel and thinly slice the red onion. Thinly slice the portobello mushrooms. Peel and grate the garlic (or use a garlic press). Finely chop the parsley (stalks and all).
Pour half the the balsamic vinegar into a bowl with the olive oil for the dressing (see pantry for amount) and season with salt and pepper. Mix together and set aside until ready to serve.

When your pan of water is boiling, add the penne and bring back to the boil. Cook until tender, 12 mins.
Once cooked, drain in a colander and pop back into the pan. Drizzle with oil and stir through to stop it sticking together. Set aside, off the heat.

While the pasta cooks, heat a drizzle of oil in a frying pan on medium heat. Once hot, add all the mushrooms and cook until browned, stirring occasionally, 6-7 mins.
Once browned, reduce the heat to medium-low and add the onion. Cook, stirring frequently, until softened, 5-6 mins.
Stir in the garlic and season with salt and pepper. Cook for 1 min, then add the remaining balsamic vinegar and cook until evaporated, 1 min more.

Pour the water for the sauce (see pantry for amount) into your frying pan and stir in the veg stock paste.
Increase the heat and bring to the boil, then reduce the heat to low and simmer until reduced, 5-6 mins, stirring occasionally.
Stir in the creme fraiche until well combined, then bring back to the boil and add a good grind of pepper. Remove from the heat.

Add the cooked pasta to the sauce along with three quarters of the hard Italian style cheese and three quarters of the parsley.
Stir everything together. Taste and add more salt and pepper if needed.

Spoon your mushroom penne into bowls and sprinkle the remaining cheese and parsley on top.
Add the rocket to the balsamic dressing and toss together. Serve on top of the pasta finished with another good grind of pepper. Enjoy!