Vanilla Citrus Soufflés

Name: Vanilla Citrus Soufflés
Ingredients: 6 tablespoons/75 grams granulated sugar; 2 tablespoons pink grapefruit zest plus 5 teaspoons pink grapefruit juice (from 2 grapefruits); 1 vanilla bean (optional; see Tip); Softened unsalted butter, for greasing ramekins, plus 1½ tablespoons unsalted butter, at room temperature; 3 large egg yolks plus 4 egg whites (see Tip); 2 tablespoons all-purpose flour; 1/4 teaspoon coarse kosher salt (such as Morton) or 1/2 teaspoon kosher salt (such as Diamond Crystal); 1/2 teaspoon freshly cracked black pepper; 3/4 cup/180 milliliters whole milk; 1/4 cup/60 milliliters heavy cream; 1/8 teaspoon cream of tartar