Mix cream, milk, half of the sugar in a saucepan over medium high heat. Scald the mixture (look for tiny bubbles to form on edge of the surface), but do not bring to a boil. Meanwhile whisk together the egg yolks and sugar. The sugar will start cooking the eggs, so do this just before the milk reaches scalding. Slowly temper the milk mixture into the egg mixture by adding a ladle at a time while whisking continuously, until it is all combined. Add vanilla or other flavorings you are using.
Pour custard into a baking dish prepared with pieces of bread. If you are adding things like cranberries or chocolate chips, have these ready in the dish along with bread. Make sure to pour the custard over the whole thing so that all the bread has been drenched, although it will not all be covered. Add any other toppings you desire.
Soak for at least 30 minutes or even overnight. Bake at 325°F for about an hour or until the center is set. Cool completely before cutting into as this helps the custard set. Eat warm or cold. To reheat, warm for 30 minutes at 300°F. Store leftovers in the fridge.