Preheat the oven to 350F (180C).

Place the onions and tomatoes on a baking sheet lined with foil.

Roast the onions and tomatoes for 20 minutes.

Add the garlic to the baking sheet.

Continue roasting for another 20 minutes, or until the garlic is soft and the onions are golden brown.

Darkly toast the bread in a toaster.

Transfer the roasted vegetables to a blender.

Add the toasted bread to the blender.

Puree the mixture until smooth, adding vegetable stock as needed to achieve a thick paste consistency.

In a large pot or Dutch oven, combine the vegetable paste with the remaining vegetable stock.

Add the diced parsnips and potatoes to the pot.

Bring the stew to a simmer over medium heat.

Cook until the parsnips and potatoes are tender, about 20 minutes.

Stir in the cooked fava beans and corn.

Season with salt and pepper to taste.

Simmer for an additional 5 minutes to heat the beans and corn through.

Stir in the chopped parsley.

Serve hot.