Preparation

For the crust

1. Preheat the oven to 350°F. Lightly coat the inside of an 8x8-inch baking pan with the tablespoon of cold butter; reserve.
2. Put the graham cracker crumbs, sugar, and salt in the bowl of a Cuisinart® stand mixer. Attach the flat mixing paddle. Mix on Speed 2 to combine, about 30 seconds.
3. With the mixer running, slowly add the melted butter, and mix until the crumbs are totally coated, about 2 minutes.
4. Transfer the crumbs to the prepared pan, and press into an even layer. Use the bottom of a glass or custard cup to firmly tamp down the crust.
5. Bake until the edges start to brown, 10 to 15 minutes.
6. Remove from the oven, and place on a wire rack to cool completely.

For the filling

1. Add the eggs and sugar to the bowl of a Cuisinart® stand mixer. Attach the flat mixing paddle, and mix on Speed 2 until just smooth, about 1 minute. Add the sweet potato purée, heavy cream, vanilla extract, salt, cinnamon, ginger, cloves, and nutmeg, and mix on Speed 2 until completely smooth.
2. Pour the sweet potato mixture over the cooled crust. Bake for 50 minutes at 350°F until the filling is set but still slightly jiggly in the center. Let cool completely at room temperature.

For the topping

1. Add the egg whites and sugar to a bowl set over a saucepan of simmering water. While continuously whisking, heat the egg whites and sugar until the egg whites are warm and sugar is dissolved. Remove from the heat.
2. Transfer the egg white mixture to the bowl of a Cuisinart® stand mixer, and then add the vanilla and cream of tartar. Attach the whisk attachment, and mix on Speed 9 until stiff peaks form and the meringue is glossy.
3. Spread the meringue over the cooled sweet potato layer. Using a kitchen torch, lightly toast the topping until golden brown.*
4. Cut into squares and serve or refrigerate for up to 2 days until ready to serve.

* Alternatively, toast the topping under a broiler. Keep a close eye while doing this because the meringue will brown quickly.