Very lightly oil a 12 x 16-inch baking sheet. Combine the water, vegetable broth, salt, polenta and the olive oil in a cooking container, either a pressure cooker, microwave-safe bowl, or heavy soup pot.
To cook in an Instant Pot pressure cooker: Put the vegetable broth and water, polenta, olive oil, and salt in the Instant Pot. Do not stir. Lock lid. Sent the top Vent to seal. Cook on Porridge setting with time adjusted to 7 minutes. Natural pressure release for 10 minutes, then vent to release the pressure completely.
To cook in microwave oven: Cover and cook on highest power for five minutes. Stir, cover again and cook for another five minutes. Stir in the nutritional yeast, cover and cook for three more minutes.
To cook stovetop: Bring 2 cups water and 2 cups vegetable broth to a boil in a medium-size heavy sauce pan over high heat. Add the salt and olive oil. Slowly pour cornmeal into the hot liquid, stirring with a wire whisk or wooden spoon. In 2 to 3 minutes, when the polenta begins to thicken, reduce heat to low. Cook for at least 45 minutes, giving it a stir every 5 minutes or so. When it is very thick, stir in the nutritional yeast.
Quickly pour the soft polenta into the prepared baking sheet and spread into an even layer before it cools. It will be a bit less than ¼-inch thick. Cover and chill until firm.
To crisp the polenta: Preheat oven to 450 °F. Turn the polenta out onto a cutting board and cut into 20 portions, approximately 3-inch square. Line the baking sheet with parchment paper. Arrange the cut squares on the parchment and brush them lightly with olive oil. Bake 25 to 30 minutes, until you see a hint of golden brown around the thinnest edges. Remove from the oven but keep warm.