- 1 1/2 pounds medium-size sweet potatoes
- 1 tablespoon vegetable oil
- 3/4 cup firmly packed light brown sugar
- 1/2 teaspoon ground cinnamon
- 1/4 teaspoon freshly grated nutmeg
- Pinch of salt
- 1 teaspoon pure vanilla extract
- 3 large eggs
- 3 cups milk
- 2 1/2 cups graham cracker crumbs
- 2 cups pecan pieces
- 3/4 cup (1 1/2 sticks) unsalted butter, melted
- 8 ounces semisweet chocolate morsels
- Preheat the oven to 375°F.
- Rub the sweet potatoes with the vegetable oil and place on a baking sheet lined with parchment paper. Bake until fork-tender, 1 to 1 1/2 hours. Remove from the oven and let cool, then peel and mash in a large bowl.
- Add to the mashed potatoes the brown sugar, cinnamon, nutmeg, salt, vanilla, eggs, and 2 1/2 cups of the milk and mix well. Set aside.
- Lower the oven temperature to 350°F.
- Combine the graham cracker crumbs and pecan pieces in a food processor and process for about 1 minute, to make a fine meal. With the motor running, gradually pour the melted butter through the feed tube and process for 1 minute. Transfer the crumb mixture to a 13 X 18-inch baking pan and, using your fingers, firmly press the crumbs evenly onto the bottom and up the sides of the pan.
- Pour the sweet potato mixture into the crust and spread evenly with a rubber spatula.
- Put the chocolate morsels and the remaining 1/2 cup milk in a medium-size saucepan over medium heat and stir constantly until the chocolate melts and the mixture is smooth. Spoon the chocolate in three rows, about 2 inches apart, lengthwise over the sweet potato mixture. Then, with a knife, make a zigzag pattern to marbleize the chocolate and the sweet potato mixture.
- Bake until the edges are browned and the filling is set, 20 to 25 minutes. Remove from the oven and let cool completely. To serve, cut into bars.