Not-too-sweet Baked Dark Chocolate Custard

About 1 ounce of a good quality dark bittersweet chocolate (I use 5-6 squares of TJ Pound Plus)
2 cups whole milk
Optional variation:  1/4 c heavy cream + 1-3/4 cup whole milk OR
1/4 c (or more) heavy cream + 2 shots expresso or 1/4 cup strong coffee  + 1-1/2 cups whole milk  OR
any combination of the above that equals about 2 cups liquid of mostly milk, cream, or half & half.
Needless to say, using some heavy cream increases the silky richness of the custard.  I like Trader Joe’s heavy whipping cream in the plastic pint bottle; it has a high butterfat content, isn’t ultra-pasteurized, and the price is great.  I also sometimes use Organic Pastures raw heavy cream, especially if it has started to sour a bit.  It is really thick, yummy, and high in butterfat, too, but oh so expensive.
1 teaspoon vanilla (or other flavored extract, such as orange, almond, hazelnut, or anise)
pinch of salt
2 eggs, beaten until mixed
Optional:  sugar or other sweetener such as Splenda, maple syrup, or a flavored syrup (like Monin or Da Vinci), about 1 to 3 Tablespoons, to taste
(I sometimes use 1-2 squirts of flavored sugar-free Da Vinci syrup or Splenda granular if I am adding the espresso, and little or no extra sweetener if not, YMMV)
1-1.5 qt oven-proof casserole (I like Corning)
baking pan for water bath (bain marie)
Put water on to heat for water bath (bain marie).  Set oven rack to middle position and preheat to 300° F.  If I bake in my large toaster oven, I set the rack at the lowest position.
Melt the chocolate in a 1 or 1.5 qt  oven-proof casserole in the microwave on medium power, taking care not to cook or burn the chocolate (or melt over a double boiler).  Whisk to melt evenly and get rid of lumps.
Slowly drizzle heavy cream into melted chocolate, whisking to mix evenly.  Be sure not to dump in cold cream or milk; it will “seize” and cool the warm chocolate, which interferes with mixing.  Then slowly whisk in the milk, espresso/coffee (if using), beaten eggs, then remaining ingredients.  At this point I taste to determine if I need to make it sweeter (frankly, I don’t freak out about raw eggs much anymore but you can also taste it first, then add the eggs last).  If it is not sweet enough for your taste, add 1-3 Tablespoons of your sweetener of choice.
When everything is whisked together and is smooth, place casserole in baking pan and place both on middle rack of oven.  Pour hot water into baking pan about half way up the side of the casserole, being careful not to pour water into custard.
Carefully push oven rack back into oven without sloshing the hot water!  Bake at 300°F approximately 1 hour and 10 minutes until set at edges and softly set in center (time may vary by 5 minutes either way).    Remove casserole from oven and set on cooling rack.  Center of custard will set up a bit more as the custard cools.
Do not serve hot.  Serve slightly warm,  at room temperature, or chilled, with fresh whipped cream (I make unsweetened whipped cream in an iSi cream whipper).
Store leftovers covered in the fridge.  Great for breakfast, too!
Note:  The custard can also be baked in individual custard cups or ramekins, also in a water bath (bain marie).  The baking temp is the same, but reduce the time to probably about 45 minutes or so.  Check for doneness with a knife inserted near halfway between cup edge and center; custard is set when knife is clean when removed.