Gratin potato - Potatoes New Zealand

Ingredients

• 800g mashing potatoes, washed and peeled
• 300 ml cream
• ½ white onion, sliced
• 1 bay leaf
• 3-4 sprigs of thyme, finely chopped
• 2 tsp flaky sea salt
• 20g melted butter
• 2-3 butter wrappers