Bring the vegetable stock to a boil in a large saucepan. Season with salt and pepper and add several larger mushrooms to the stock to fortify it. Lower heat and cook mushrooms and stock for 6 - 10 minutes.
Meanwhile in another pan, render the Pancetta at a low heat until thoroughly cooked then remove the meat from the pan and squeeze all oil out with paper towels. You can also use regular bacon or turkey bacon or none at all, depends upon your taste and if you’re vegetarian or not.
Ensure you still have 4 1/2 cups of liquid, if not add water and a bouillon cube to the stock. Remove all the mushrooms with a slotted spoon, draining the liquid and reserve off to the side with the rest of your smaller mushrooms.
Ensure you have a whisk and a wooden spoon or equivalent at the ready and a cookie sheet lined with parchment paper! Bring the stock back to a boil and add the polenta to the fortified stock in a thin stream, whisking continuously into the boiling liquid. As soon as it re-boils, reduce the heat immediately and swap your whisk for the wooden spoon. Stir in the pancetta, boursin, parmesan cheese and sun-dried tomatoes (optional) and simmer the polenta until thick and porridge-like. WARNING the polenta may start to splatter volcanically, if this happens, remove from the burner and keep stirring until it calms down.
Spread the polenta evenly over the lined cookie sheet to about ½ to ¾ inch thick. Use the wooden spoon to spread evenly and smooth the top of the polenta. Leave this to cool for the next 20 – 30 minutes while you prep and cook the remaining items. If necessary, the polenta can be prepared up to a couple days in advance.
Cut the polenta into long triangles and re-warm or pan-fry until lightly golden and crispy. I’ve tried it both ways, and prefer leaving the polenta as-is and foregoing the extra calories added to the dish by pan-frying. In either case you’ll be serving each guest a couple triangles, so arrange a couple on each plate and prepare them for the delicious mushroom stir-fry!
Have some long matches or a BBQ lighter and the marsala wine open and at the ready. Put a 60/40 mix of vegetable oil to olive oil in a frying pan and heat on medium heat to the smoke point. Add all the mushrooms and stir briskly for about 1 minute salting them with some kosher or sea salt. Add the shallots (or pearl onions), garlic, wild garlic shoots (or green onion) and chopped thyme and stir in to the mix. Pour in the marsala wine and immediately light the wine with a long match or lighter to quickly burn off the alcohol. Add the butter and stir into the marsala to create a creamy sauce. Season with more sea salt and freshly ground pepper to taste. Stir-fry until mushrooms appear golden and cooked.
Divide the mushroom stir-fry evenly amongst the plates, placing the mushrooms on top of the polenta and serve immediately.