Spring Greens Salad with Warm Crème Fraîche and Black Cocoa

Name: Spring Greens Salad with Warm Crème Fraîche and Black Cocoa
Ingredients: 1 grapefruit; 1 orange; 1 lemon; 1 cup distilled white vinegar; 1¼ teaspoons sugar; 1 cup vegetable oil; 1 tablespoon finely ground dried lemon verbena; ½ cup all-purpose flour; 2 tablespoons sugar; 2 tablespoons black cocoa powder; 1 tablespoon Dutch-processed cocoa powder; ⅛ teaspoon baking soda; Kosher salt; 4 tablespoons (½ stick) unsalted butter, room temperature; ⅓ cup crème fraîche; Freshly ground black pepper; 8 cups mixed greens (such as mâche, arugula, red chard, red romaine, and/or red and green oak; Black cocoa powder can be found at some specialty foods stores and online.