Cheesy Cauliflower Gratin

Name: Cheesy Cauliflower Gratin
Prep time: 15 min
Cook time: 50 min
Total time: 1 h 5 min
Cuisine: American
Ingredients: 1 medium head cauliflower (cut into florets, about 6 cups); 8 ounces cream cheese (at room temperature); ½ cup mayonnaise (I like Duke's or Blue Plate); 2 cups cheddar cheese (shredded); 1 teaspoon garlic clove (minced); ¼ teaspoon salt; ¼ teaspoon black pepper; ¼ teaspoon cayenne pepper; ¼ teaspoon dry mustard; ⅔ cup panko bread crumbs; chopped green onions for garnish