- Pre-heat oven to 350 degrees.
- Combine cream and milk together with aromatics in non-reactive pot. Place over medium heat and bring to a simmer. Remove from heat and let steep for 30 minutes. Strain milk mixture and return to pot. Bring to a simmer over medium heat.
- Add roux to pot while whisking. Return to a simmer, and season to taste with salt.
- Fill large pot ⅔ full of salted water. Bring to boil over high heat. Place cauliflower in pot and cook for 3 minutes after water returns to boil. Strain and rinse with cold water.
- Toss mushrooms in olive oil, salt, and Calabrian chilies. Roast in oven until caramelized.
- Sweat onions in saute pan over medium heat with oil, salt, and water.
- Assemble veggies in baking dish with cauliflower on top. Pour thickened cream mixture over top until barely covered. Place in oven and bake until bubbly.