Bring the cream and milk to a simmer in a saucepot. In a separate bowl, whisk the egg yolks, brown sugar, cornstarch, and vanilla. While whisking, slowly pour in the hot cream, then pour the entire mixture back into the pot. Whisk the custard over medium heat until it has thickened and just begins to bubble, about 3 minutes. Pour the cooked custard through a strainer int