Sweet potato gratin

Ingredients

• 1.5 kilogram kumara, peeled, chopped
• 1/4 cup (60ml) milk
• 2 eggs, lightly beaten
• 30 gram butter, plus 20g extra
• 1/2 teaspoon ground cinnamon
• 1/2 teaspoon grated nutmeg
• 1/2 cup (40g) grated parmesan
• 1/4 cup (60g) grated swiss-style cheese, such as jarlsberg
• 1/2 cup (35g) fresh breadcrumbs