Finely chop the onion.

In a saucepan, combine the chopped onion and 1/4 cup of water.

Cover the saucepan and simmer over medium heat for 5 minutes, or until the onion is tender.

Add the remaining 4 cups of water, dried rosemary, dried thyme, and salt to the saucepan.

Bring the mixture to a boil over high heat.

Reduce heat to medium-low and gradually add the cornmeal, stirring constantly to prevent lumps from forming.

Continue stirring and cooking the polenta until it thickens to a porridge-like consistency, approximately 15 to 20 minutes.

Lightly spray a baking sheet with nonstick cooking spray.

Spread the cooked polenta evenly onto the prepared baking sheet, creating a layer approximately 3/4 inch thick.

Allow the polenta to cool completely, or refrigerate for up to 24 hours to firm it up.

Preheat the oven to 375°F (190°C).

Drizzle the olive oil evenly over the surface of the polenta.

Use a brush to spread the olive oil, ensuring the entire surface is coated.

Sprinkle the freshly grated parmesan cheese evenly over the polenta.

If desired, cut the polenta into squares or triangles and slightly separate the pieces for crispier edges.

Bake in the preheated oven for 12 to 15 minutes, or until the polenta is hot and the cheese is melted and slightly crispy.

Remove the baked polenta from the oven and serve hot.