Cheesy Chicken and Cauliflower Gratin

Ingredients

• 1 head (14 oz or 400 g) cauliflower, cut into small florets
• 2 cups (10 oz or 300 g) cooked chicken breast, shredded
• 1/4 cup (2 oz or 60 g) unsalted butter
• 1/4 cup (2 oz or 30 g) plain flour
• 1 cup (4 oz or 120 g) cheddar cheese, shredded
• 1/2 cup (2 oz 60 g) Parmesan cheese, shredded
• 1/4 teaspoon (0.5 g) cayenne pepper
• 2 teaspoons (10 g) wholegrain mustard
• 2 cups (8 fl oz or 500 g) milk, room temperature
• a dash of salt
• 1/4 tsp. (0.5 g) freshly ground black pepper