Chocolate gets a reputation of being difficult to work with, because it can seize up in an instant, and you may as well toss it out and start over at that point. Again, though, with a little know-how, you can get around this. If you put your liquid into your chocolate before you melt it, it will be beautiful. If liquid gets into your chocolate as it melts, it will seize up, get grainy, and you can forget about it.
Give it a little stir, over medium heat, while you turn your attention to the eggs. This is another turning point of the cake. You have to be sure not to get any egg yolk into your whites. What a lot of people do is separate their eggs over one bowl, then put the yolk into another bowl, and the white into a third bowl. I hate doing extra dishes, so I just use two bowls, but I understand that if I get any egg yolk into my whites, I have to start over.
If you get anything into your egg whites, they will not whip properly, and you will just be wasting your time if you try anyway. But, really, as long as you're careful, you should be fine.
Once your chocolate is 90% melted, turn the heat off, and let the residual heat finish melting the chocolate. After the heat is off, take your bowl off of the pot, but be careful; there will be some steam coming up, and your bowl will be hot. Let your melted chocolate cool down to room temperature, for about 20 minutes or so. While your chocolate cools, preheat your oven, to 350*, thoroughly butter your dish, and run the 2 Tbs of sugar around the dish, making sure you get it all over.
Once your chocolate has cooled to room temperature, add in your lightly beaten egg yolks, and stir to combine. Set this aside.
Now then, lets turn our attention to the egg whites. Beat your egg whites and cream of tarter on medium-high, until soft peaks form, about 2 minutes. Once soft peaks have formed, slowly add in the 1/4 C of sugar, and continue to beat until stiff peaks form, about another 5 minutes.
You want the egg whites to be glossy, but when you take the whisk out, the egg whites will hold the shape of a peak.
Once your egg whites look like this, take a bit and just mix it up into the chocolate mixture. Don't worry about deflating the egg whites, just mix it up into the chocolate, to help loosen it up, and make folding in the rest of the egg whites easier.
Once that initial dollop of egg whites has been mixed in, gently fold in half of the remaining eggs. It doesn't have to be completely mixed in with the chocolate; as a matter of fact, I would gently fold the mixture, until it is about 75% mixed in, and then add the remaining egg whites, again, folding in gently. Since the egg whites are what make the cake puff up, you want them to maintain the air that you have worked to incorporate, so be gentle when you're folding them in.
Once you have mixed in the egg whites about 80%, pour everything into the prepared dish, and set it on a baking sheet.
Place it in the oven, and let it bake for 30-35 minutes. It really is that simple. I let mine bake for 35 minutes, then pulled it out, and gave it a light dusting of powdered sugar. This cake forms a soft crust from the egg whites, that you break into as you dip into as you scoop it out. The inside is just a little runny (think chocolate melting cake), and is perfect with a cup of coffee, and a scoop of ice cream, or some whipped cream.