Prep the oven. Position a rack in the center of the oven and preheat to 300°F.
Make the custard base. In a medium bowl, whisk together the egg, egg yolks, sugar, and salt.
Heat the cream and vanilla. Pour the cream into a medium, heavy-bottomed saucepan. Use the tip of a sharp knife to slice the vanilla bean pod lengthwise and scrape its seeds over the cream. Add the pod to the cream, too. Bring to just under a boil over medium heat, whisking continuously.
Strain the cream, then slowly whisk it into the custard base. Place a fine-mesh sieve over a large liquid measuring cup and quickly pour the cream over it to strain out the vanilla bean pod. Discard the pod. Slowly pour the strained cream into the custard base, whisking the custard base continuously. Whisk in the orange liqueur. Once combined, hold the sieve over a 9-inch deep-dish pie pan and pour the custard through the sieve to fill the pan.
Bake the creme brulee. Place the pan of creme brulee in a large roasting pan. Make a water bath by filling the pan with enough boiling water to reach at least half way up the sides of the creme brulee pan. Bake for 50 to 60 minutes, or until the edges of the creme brulee are set but its center wobbles ever so slightly.
Cool and chill the creme brulee. When done, remove the creme brulee from the water bath and cool completely on a wire rack. Loosely cover the top with plastic wrap and refrigerate for at least 4 hours, preferably overnight. The creme brulee can be refrigerated for up to 5 days.
Torch the creme brulee. When ready to serve, remove the creme brulee from the refrigerator, discard the plastic wrap, and place on the center of a sheet pan. Let thaw slightly while you preheat the oven. Position a rack as close to the broiler as possible (preferably, on the top rack of your oven, at least 4 to 6 inches away from the broiler) and preheat on high for 10 minutes.Sprinkle the Demerara sugar evenly on top of the creme brulee. Broil for 5 to 10 minutes, or until the sugar melts completely and most of it caramelizes, rotating the pan occasionally to even the browning. Cool on a wire rack for 1 minute to allow the sugar to harden, then serve immediately.