Ultimate Creamy Cauliflower Gratin Sunday Roast Side Dish

Ingredients

• 1 large head Cauliflower (approx. 1 kg / 2.2 lbs)
• 1 litre (4 cups) Water, for blanching
• 1 Tbsp (15 ml) Salt, for blanching
• 50 g (4 Tbsp / ½ stick) Unsalted Butter
• 50 g (½ cup) All-Purpose Flour
• 600 ml (2 ½ cups) Whole Milk
• ½ tsp Nutmeg, freshly grated
• ½ tsp Dijon Mustard
• 1 tsp Fine Sea Salt
• ½ tsp Freshly Ground Black Pepper
• 150 g (1 ½ cups) Sharp Cheddar Cheese, grated (divided)
• 50 g (½ cup) Gruyère or mature Swiss Cheese, grated
• 50 g (½ cup) Panko Breadcrumbs
• 1 Tbsp Olive Oil or Melted Unsalted Butter