Two-potato gratin with Maille Mustard - La Maison Maille

Ingredients

• 2 Sweet potatoes
• 2 Russet potatoes
• ½ Stick of butter
• 2 tbs (16 g) Flour
• 2 cups (480 ml) Milk, room temperature
• 1 tsp (5 g) Maille Dijon Original Mustard
• 1 tsp (5 g) Maille Old Style Mustard
• 1 cup (120 g) Gruyere cheese, grated, plus extra for topping
• 1 tsp (1 g) Fresh thyme, chopped
• 1 tsp (1 g) Fresh rosemary, chopped
• 1 tbs (15 g) Salt
• 1 tsp (5 g) Freshly cracked black pepper
• Pinch of nutmeg