Preheat the oven to 300°F (150°C). Place six 3⁄4-cup (6–fl oz/180-ml) custard cups or ramekins in a large roasting pan. Set a fine-mesh sieve over a large glass measuring cup. Bring a kettle of water to a boil.
In a small heavy-bottomed saucepan, combine the cream and granulated sugar. Using the tip of a knife, scrape the vanilla seeds into the cream. Add the vanilla bean pod to the cream mixture and bring to a simmer over medium heat. Turn off the heat, cover the pan, and let steep for 15 minutes.
In a medium bowl, whisk the egg yolks until well blended. Return the cream mixture to a simmer over medium heat. Slowly add the hot cream mixture to the yolks, whisking constantly. (If using vanilla extract, stir into the custard.) Immediately pour the mixture into the sieve.
Scatter 1–2 teaspoons of ginger in each cup. Divide the custard among the cups and add enough hot water to the pan to come halfway up the sides of the cups.
Bake the crème brûlées until set but the centers jiggle when the cups are gently shaken, about 25 minutes. Using a metal spatula, transfer the ramekins to wire racks. Let the crème brûlées cool for about 30 minutes. Cover and refrigerate for at least 3 hours or up to 2 days.
Press the brown sugar through a fine-mesh strainer onto the crème brûlées, covering the surfaces completely. Using a kitchen torch, hold the flame 2 inches (5 cm) above the surface and heat until the sugar melts, bubbles, and browns, about 2 minutes. Alternatively, preheat the broiler. Place the ramekins on a rimmed baking sheet and place about 2 inches (5 cm) from the heat source. Heat until the sugar melts, bubbles, and browns, watching carefully, 2–4 minutes. Refrigerate the crème brûlées, uncovered, until the filling is cold and the topping is still brittle, at least 1 hour and up to 4 hours. Serve cold.