Step 1Prepare a large steamer. Add the sweet potatoes and steam until tender, about 25 minutes. Drain if needed, then transfer to a large bowl and mash until smooth. Fold in the coconut milk, chipotle (if using) and 2 ½ teaspoons salt. Spread in an even layer in a shallow baking dish for serving.
Step 2While the sweet potatoes steam, whisk the aquafaba and sugar with an electric mixer on medium speed until opaque and thickened, about 5 minutes. Add the cornstarch and cream of tartar and whisk on medium-high speed until very stiff peaks form and the mixture has an almost taffy texture, about 15 minutes.
Step 3Dollop and swirl the meringue all over the sweet potatoes. Using a kitchen torch, brown the topping.