Preheat the oven to 375 degrees Fahrenheit. Place the sweet potatoes on a lipped baking sheet, leaving at least 1 inch of space between the potatoes, and roast them whole, skin on, until soft when pierced with a skewer, about 1 hour and 15 minutes. Set aside and allow to cool for 3 hours. At this point, the skins will have loosened a bit, and you can peel the skin off in pieces with your fingers.

Peel the sweet potatoes completely, cut them into 1.5-inch thick rounds, and place them on a large casserole dish or lipped baking sheet, cut side facing up. Try to keep the tops of the sweet potatoes cut flat across, because if they're at an angle the meringue may slide off the top while they're toasting in the oven. Cover and set aside.

While the potatoes are cooling, prepare the nuts. Melt the butter and sugar in a medium-sized frying pan over medium heat, stirring to incorporate the sugar. Once the sugar has melted smooth and is no longer granular, add the nuts and stir to coat them in the mixture. Let them sit in the pan for a couple minutes until they start smelling slightly toasty, then stir it up again. Repeat this process until most of the nuts are lightly browned and toasted on part of their surface and the pan is very aromatic with the smell of toasted nuts. Be careful NOT to burn them, and turn down the heat immediately if the pan begins smoking.

Remove the pan from the heat and empty the mixture onto a large baking sheet lined with parchment paper. Smooth it out so the nuts are in one layer, then immediately sprinkle the salt and rosemary over the nuts (it's important to do this while the syrup is still hot and sticky). Let them cool to room temperature, then break any clumps of nuts apart with your hands and set them aside.

Once the nuts have been prepared, and the sweet potatoes are cooled, peeled, and cut into rounds, you can start getting the Italian Meringue prepared.

Preheat the oven to 400 degrees Fahrenheit. Heat the sugar and water in a small saucepan over medium low heat until dissolved. Raise the heat to high and wait until the syrup reaches 235 degrees Fahrenheit, making sure to NOT stir the mixture.

While the syrup is boiling, beat the egg whites in the bowl of a stand mixer fitted with the whisk attachment at medium high speed until there's little bubbles at the top of the egg white mixture. Add the cream of tartar, then continue beating at medium high speed until soft peaks form. Stop the mixer until the syrup has reached the right temperature.

When the syrup is ready, turn the mixer on medium high speed and begin adding the syrup to the egg white mixture in a thin steady stream. Continue beating until the meringue is glossy and holds a stiff peak.

In a small pot, make the maple butter drizzle by heating the butter with the maple syrup and salt until the butter is melted. Quickly and lightly brush the sweet potatoes with half the mixture, then use a spoon to top each sweet potato round with a dollop of the meringue. (For a more decorative meringue application like the one pictured, use a pastry bag with a large round pastry tip to pipe out the meringue onto the tops of the sweet potato rounds).

Place the pan in the oven and toast until the meringue is lightly golden, keeping a very close eye so as not to burn them, about 4 to 7 minutes. (You can also toast the meringue with a culinary torch, if you have one). Remove from the oven, drizzle with the remaining maple butter mixture, sprinkle with the candied rosemary pecans, and serve.