Alex Switzer of St. Jude Children’s Research Hospital, Memphis, TN
Note: This is a two day process. The bulk of the work is done on day 1. Day 2 is just slicing, reheating, and making the caramel.
Ingredients:
4 large sweet potatoes
1 1/2 cups shredded Gruyère or Swiss cheese
For the custard:
1 quart heavy cream
3 eggs
2 teaspoons salt
1 tablespoon finely chopped sage
For the spice mix:
2 tablespoons salt
1/2 teaspoon black pepper
2 teaspoons brown sugar
1/2 teaspoon cayenne pepper
For the caramel:
1 cup toasted pecan pieces
1 cup brown sugar
2 tablespoons water
1 tablespoon butter
Method:
Day 1:
Preheat your oven to 350F.
Make the spice mix. Thoroughly mix the 2 tablespoons of salt, 1/2 teaspoon of black pepper, 2 teaspoons of brown sugar, and the 1/2 teaspoon of cayenne pepper. Set aside.
Mix the custard: Mix the heavy cream, eggs, sage and 2 teaspoons of salt together thoroughly and set aside.
Rinse the sweet potatoes and then peel off the skin. Use a mandoline and very carefully cut the potatoes lengthwise into 1/4” slices. Reserve slices on a paper towel. You don’t want to reserve the sliced sweet potatoes in water because we want to preserve any starchiness they may have.
Liberally pan spray a bread loaf pan or a similar pan, roughly 9” x 5” x 2.75”. Start by placing sweet potato slices in the bottom of the pan in a scaled pattern in a single, even layer. Between each layer add a pinch of your spice mix and about a tablespoon of your shredded cheese. Repeat, and push down on each subsequent layer of potatoes to spread them evenly until you reach about an inch below the lip of the pan.
Once all of the potatoes are layered, slowly start adding your custard, allowing each pour time to fall down into the cracks. You can help this process by gently pulling the sides of the potato away from the pan to add more clearance. When the custard begins to cover the top of the potatoes, do not add any more.
Liberally pan spray a sheet of aluminum foil and cover the pan sprayed side down tightly. Put the pan on a larger half sheet tray to avoid any boil over from the cream going onto the bottom of your oven.
Cook your sweet potato au gratin for an hour. Then, take off the foil and check the tenderness with a pairing knife. Cook longer if the knife doesn’t fall through the au gratin easily.
Once the potatoes are cooked, put the au gratin back in the oven a cook uncovered for another ten minutes. Remove let it cool at room temp for 30-45 minutes.
Once the au gratin has cooled, place a piece of food film on top of it and put an evenly distributed weight atop the film, and let sit in the fridge over night.
Day 2
Preheat oven to 375F.
Take the au gratin out of the fridge and release the sides from the pan with a flat, metal spatula, and turn upside down onto a cutting board. Cut cross sections 2”-3” wide and place flat on a liberally sprayed sheet pan. You can line the pan with parchment paper if you want.
Heat the au gratin in the oven until bubbling.
Meanwhile, make the caramel. Put your toasted pecans, water, and brown sugar with a small pinch of salt into a sauté pan over medium heat and slowly bring to a simmer. Keep an eye on it while the water evaporates and the sugar begins to caramelize. When the mixture has reduced to a slightly loose caramel, turn off the heat and add the butter, stirring thoroughly. BE EXTREMELY CAREFUL AS THE CARAMEL WILL BE VERY HOT AND STICKY!
Optional: You can fry a couple sage leaves in a couple tablespoons of vegetable oil for garnish. Be sure to drain the leaves on a paper towel before using.
When the au gratin is bubbling, use a metal spatula to transfer each slice to a plate. Cover with a spoonful of the pecan caramel.