Preheat oven to 325°F (165°C). Position a rack in the middle of the oven.

In a medium bowl, combine the egg yolks and 6 tablespoons of the granulated sweetener. Beat to combine. Set aside.

In a small saucepan over medium heat, heat the cream until bubbles begin to simmer along the edge of the pot.

While whisking, pour the warm cream into the yolk mixture in a thin, slow, steady stream. Whisk in the vanilla extract and 1/4 teaspoon salt.

Pour the mixture through a fine-mesh strainer into a pitcher or liquid measuring cup, then fill the 6 ramekins evenly and place them in a 9 by 13-inch baking dish. Place the baking dish on the center rack in the oven, then carefully pour enough of the hot water into the baking dish to come halfway up the sides of the ramekins.

Cover the baking dish with aluminum foil, then bake until the brûlées have a firm surface and wobbly center, 50 to 55 minutes.

Carefully remove the ramekins from the water. Let cool at room temperature for 30 minutes, then refrigerate to cool completely, 4 hours to overnight.

To serve, carefully dab the tops of the custards with paper towel to remove moisture. Evenly sprinkle the tops with the remaining granulated sweetener, about 1½ teaspoons on each. Gently shake the ramekins to evenly distribute.

Place an oven rack in the highest position. Place the ramekins on the rack. Turn on the broiler and broil, watching closely and rotating the ramekins frequently for even broiling, until the sugar is golden brown and bubbling, 5 to 10 minutes. Transfer to the fridge to cool for 10 to 30 minutes. Serve.