Heat 1 tablespoon of oil in a large frying pan on medium heat. Add the tempeh pieces and fry gently for 2-3 minutes on each side or until lightly browned.
While the tempeh is cooking, bring a large pan of salted water to the boil and cook the pasta according to package instructions (usually 10-12 minutes). The sauce should be ready around the same time as the pasta.
Once the tempeh is a light golden-brown on both sides, remove from the pan and set aside. Using the same pan, heat ½ tablespoon of oil on medium/high heat and add the mushrooms. Stir regularly for 3-4 minutes until starting to colour.
Once the mushrooms have browned slightly, reduce the heat to medium and add the garlic, salt, and pepper. Cook for 2 minutes.
Next, add the vegan cream, dried tarragon, nutritional yeast, and cooked tempeh. Stir well, adding small ladles of pasta cooking water to the pan as necessary to keep the sauce fairly loose.Note: Homemade cashew cream will likely require more water than e.g. a shop-bought oat cream – just keep an eye on it and add as much pasta cooking water as needed. This water will be starchy, which helps to keep the sauce at a nice consistency.
Around the same time you add the cream to the saucepan, add the broccoli pieces to the pasta pot. These will become tender during the remaining pasta cooking time (you can add the broccoli earlier if you prefer it well-cooked).
Once the pasta and broccoli are cooked through, drain them together and add to the pan with the creamy sauce. Mix well, adjust the seasoning, add a squeeze of lemon juice (optional), and serve.