Italian Herb-Roasted Mushroom and Polenta Casserole

By , Test Kitchen Director · Reviewed by AislePrompt Editorial · ·

An earthy baked casserole layering creamy polenta with sautéed mushrooms and fragrant Italian herbs for a comforting vegetarian entree. This italian-inspired vegetarian (vegetarian) ready in about 40 minutes pairs instant polenta, water, olive oil for a weeknight-friendly dinner that comes together with one pan and minimal cleanup. Each serving lands at about 320 calories and feeds 4, so it slots cleanly into a weekly meal plan and pairs well with a quick salad or grain on the side. Tap "Plan a meal with the AI" below to drop this recipe into your week and send the ingredients straight to Instacart. Nutrition values are approximate, calculated from USDA FoodData Central (fdc.nal.usda.gov) — verify against ingredient labels for any health-driven dietary plan.

Prep: 10 min Cook: 30 min Serves 4 Italian cuisine 320 cal/serving
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Ingredients

Instructions

  1. Step 1: Bring 4 cups water to a boil in a medium saucepan. Slowly whisk in 1 cup instant polenta, reduce heat to low, and cook for 5 minutes, stirring frequently until thickened and creamy.
  2. Step 2: While polenta cooks, heat 3 tbsp olive oil in a large skillet over medium-high heat. Add 12 oz sliced button mushrooms and sauté for 6-8 minutes until they release moisture and begin to brown.
  3. Step 3: Add 3 minced garlic cloves, 1 tsp dried thyme, 1 tsp dried rosemary, 1 tsp salt, and 1/2 tsp black pepper to mushrooms. Cook for another 2 minutes until fragrant.
  4. Step 4: Preheat oven to 375°F. Spread half the cooked polenta evenly in a greased 8x8-inch baking dish. Layer sautéed mushrooms over polenta, then top with remaining polenta.
  5. Step 5: Sprinkle 1/2 cup grated Parmesan cheese evenly on top and bake for 20 minutes until golden and set.
  6. Step 6: Garnish casserole with 1/4 cup chopped fresh basil before serving warm.

Equipment for this recipe

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Frequently asked questions

How long does Italian Herb-Roasted Mushroom and Polenta Casserole take to make?

Total time is about 40 minutes (10 min prep + 30 min cook). Most home cooks find this fits comfortably into a weeknight; double the batch on Sunday for two dinners.

How do I store leftover Italian Herb-Roasted Mushroom and Polenta Casserole?

Cool to room temperature within 2 hours, then store in an airtight container in the fridge for up to 4 days. Reheat covered in a 350°F oven for 10-12 minutes, or microwave at 70% power in 60-second bursts to keep instant polenta from drying out.

Can I substitute ingredients in Italian Herb-Roasted Mushroom and Polenta Casserole?

Yes — most ingredients in this recipe have flexible swaps. For oil, use any neutral high-smoke-point oil (avocado, grapeseed, refined coconut). For aromatics, dried herbs at ⅓ the volume of fresh work in a pinch. The full ingredient list is shoppable on Instacart so you can see substitutes in real time.

How do I scale Italian Herb-Roasted Mushroom and Polenta Casserole for a different number of people?

The recipe is written for 4 servings. Multiply each ingredient by (your serving target / 4). Cook time stays roughly the same up to 2x; for 3-4x batches, switch from a skillet to a sheet pan or stockpot so the food isn't crowded — overcrowding steams instead of browns.

Is Italian Herb-Roasted Mushroom and Polenta Casserole vegetarian?

Yes — this recipe is tagged vegetarian based on its ingredient list. Always cross-check labels for packaged ingredients (sauces, broths, condiments) since formulations vary by brand.

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