Best Broccoli Cauliflower Casserole Recipe - How To Make Broccoli Cauliflower Casserole

Ingredients

• Unsalted butter or cooking spray
• 2 lb. cauliflower (about 1 medium head), cut into small florets
• 2 c. water, divided
• 1 lb. broccoli (about 2 large heads), cut into small florets
• 1/2 c. cream cheese, room temperature
• 3/4 c. sour cream
• 1/2 c. coarsely chopped sun-dried tomatoes
• 3 scallions, white and green parts separated, finely chopped
• 1 clove garlic, finely chopped
• 1 tbsp. cornstarch
• 1 (1-oz.) ranch powder packet
• 1 tsp. crushed red pepper flakes (or similar spice of your choosing)
• Kosher salt
• Freshly ground black pepper
• 2 c. coarsely shredded or torn fresh mozzarella (about 16 oz.), divided
• 3/4 c. grated Parmesan (about 3 oz.)