Sweet Potato Gratin with Vanilla Bean and Bay Leaves

This was absolutely delicious and I quartered the recipe so that was plenty for two of us. It comes from a new website called Milkstreet. BTW I found vanilla beans at Costco at a great price.

• 5
  POUNDS SWEET POTATOES
• 1
  CUP HEAVY CREAM
• 4
  BAY LEAVES
• 1
  VANILLA BEAN
• ⅓
  CUP PLUS 1 TABLESPOON PACKED DARK BROWN SUGAR
• 1¼
  TEASPOONS KOSHER SALT
• ¾
  TEASPOON GROUND BLACK PEPPER
• ⅓
  CUP WHITE SUGAR
• PINCH CAYENNE PEPPER (OPTIONAL)
• Heat the oven to 400ºF with one rack in the middle position and another 6 inches from the broiler. Pierce the sweet potatoes with a fork and arrange on a rimmed baking sheet. Bake on the middle rack, turning once, until tender, 1 to 1½ hours. Let cool.
• 
  
•  Increase oven to 425ºF. While the potatoes roast, in a medium saucepan, combine the cream and bay leaves. With a paring knife split the vanilla bean lengthwise, then scrape out the seeds. Add the seeds and pod to the cream and simmer over medium high. Set aside, covered, for 30 minutes. Strain out and discard the solids.
• 
  
•  Once cooled, peel the sweet potatoes and discard the skins. In a food processor, combine half the ƒsweet potatoes and half the cream. Add 1 tablespoon of the brown sugar, the salt and pepper. Process until smooth, about 1 minute, scraping the bowl halfway through; transfer to a large bowl. Repeat with the remaining potatoes and cream, then add to the ‚first batch. Mix well, then transfer to a 13-by-9-inch baking dish. Smooth the top. 
• 
  
• In a bowl, stir together the remaining brown sugar, the white sugar and the cayenne, if using. Transfer to a medium mesh strainer, then sift the mixture over the surface of the potatoes to create an even sprinkling. Brush any sugar off the rim of the baking dish. 
• 
  
• Bake on the middle rack until bubbling at the edges, about 20 minutes. Remove from the oven, then heat the broiler. When ready, place the dish on the upper rack and broil until deeply browned and crisp, 2 to 7 minutes. Let sit for 20 minutes before serving.