We got this recipe from Bon Apetit magazine about 20 years ago. It didn't have the salt or liqueur in it, I think they add but aren't mandatory. It's just about the perfect chocolate cake, IMO. Dense, moist, and rich. It's also one of the easiest to make cakes in the world and almost foolproof. (Leaving the wax paper on the bottom or overcooking a little bit are recoverable. Dropping the cake onto the bottom of the oven when you take it out to cover it with foil isn't so great, but if you have the ingredients you can have another whipped up and in the oven in minutes.)
Almost Flourless Chocolate Cake
10 oz bittersweet (not unsweetened) or semisweet chocolate, chopped
1 cup (2 sticks) unsalted butter, cut into small pieces
5 large eggs
1 1/4 cup sugar
5 Tbsp all purpose flour
1 1/2 tsp baking powder
A couple glugs of liqueur (Grand Marnier & Chambord are nice--use what you like)
A couple pinches salt
Preheat oven to 325 degrees. Butter and flour 10 inch springform pan, and line the bottom with waxed paper. Melt together chocolate & butter, remove from heat and stir in liqueur.
Beat eggs and sugar in large bowl until well blended and starting to thicken. Sift flour, baking powder, and salt over eggs and fold in. Gradually fold in chocolate mixture, then pour into prepared pan.
Bake for 20 minutes, then cover pan with foil and bake about 30 minutes longer, until tester comes out with moist crumbs still attached (don't overcook!)
Cool in pan on rack (cake will fall). Remove cake from pan (don't forget to take off the waxed paper.) Dust with powdered sugar and cocoa.
Good with ice cream, whipped cream, unwhipped cream, fruit, or naked (you, the cake, or both.)