Richer than rich; for chocolate lovers only.

Lightly grease a 9 × 2-inch springform or round cake pan. Press evenly into the bottom of the pan:

Bake as directed in About Crumb Crusts. Let cool.

Have all ingredients at room temperature, about 70°F. Place a loaf pan or cake pan filled halfway with hot water on the bottom rack of the oven. Preheat the oven to 350°F.

Place in a small heatproof bowl:

Add:

Stir until the chocolate is melted and smooth. Beat in a large bowl, or in a stand mixer with the paddle attachment, just until smooth:

Scrape the sides of the bowl and the beaters well. Gradually add and beat until smooth and creamy, 1 to 2 minutes:

Beat in one at a time just until incorporated, scraping the sides of the bowl and the beaters after each addition:

Beat in:

Add the warm chocolate mixture and beat on low speed just until well blended. Scrape the batter into the crust and smooth the top. Place on a baking sheet and bake until the edges of the cake have puffed but the center still looks moist and jiggles when the pan is tapped, 40 to 45 minutes.

Turn off the oven, prop the door ajar with the handle of a wooden spoon, and let the cake cool in the oven for 1 hour.

Transfer to a rack and let cool completely in the pan before removing the pan ring (if a cake pan was used, do not unmold it). Cover and refrigerate for at least 6 hours, preferably 24 hours, before serving. The flavors are even more intense after 48 hours.