How to Make It
Process sugar, elecampane, and salt in a food processor until finely chopped, about 1 minute. Transfer mixture to a bowl; add cream, and stir until sugar dissolves. Cover and refrigerate 2 hours.
Meanwhile, preheat oven to 350°F. Bring honey to a boil in a small saucepan over medium, and cook until melted and reduced by one-fourth, about 3 minutes. Stir in vinegar; cook, stirring occasionally, until mixture is slightly reduced and syrupy, 3 to 4 minutes. Cool to room temperature, and refrigerate until chilled.
Pour cream mixture through a fine wire-mesh strainer into a bowl. Discard solids. Beat cream with an electric mixer on medium-high speed until soft peaks form, about 3 minutes. Chill until ready to serve.
Arrange sweet potatoes on a rimmed baking sheet, and bake in preheated oven just until fork-tender, 35 to 40 minutes.
While potatoes bake, open bottom and top vents of a charcoal grill completely. Light a charcoal chimney starter filled with briquettes (about 8 1/2 cups of briquettes). When briquettes are covered with gray ash, pour in an even layer on bottom grate of grill. (Internal temperature should be 375°F to 400°F.)
Using tongs, nestle sweet potatoes in coals, and roast until skins are charred and sweet potatoes are cooked through, 15 to 20 minutes. Transfer to a metal baking sheet, and let stand until cool enough to handle. Brush away ashes with a paper towel. Cut sweet potatoes into 3/4-inch slices and divide among 8 shallow bowls. Dollop 2 tablespoons whipped cream next to sweet potato in each bowl, and drizzle with honey gastrique. Garnish each with a sweet potato leaf and a pinch of bee pollen, if desired.