Bring a large pot of water to a boil and add the cauliflower florets. Cook for 10 to 12 minutes until the cauliflower is very soft.
Drain the cauliflower well and return it to the pot. Add the butter, heavy cream, minced garlic, salt, and black pepper.
Mash the mixture with a potato masher until it reaches a smooth consistency, then stir in the grated Parmesan cheese.
Divide the mash among four bowls. Use a spoon to shape each portion into an uneven oval that resembles a brain.
Warm the marinara sauce in a small pan over low heat for 2 minutes. Drizzle 2 tablespoons over each shaped mash.
Top each bowl with one fresh basil leaf before serving.