2 cups unsalted butter
1 cup sugar
3/4 cup strong hot coffee
1/4 cup Baileys Irish Cream, or other cream liquor
16oz semi-sweet dark chocolate
6 eggs, room temperature
6 egg yolks, room temperature
Position rack in center of oven and preheat oven to 325o F. Generously butter an 8-inch diameter springform pan. Line the bottom with parchment or waxed paper. Butter and flour the paper. Melt butter with sugar, coffee and Baileys in heavy 3 quart saucepan over medium-low heat, stirring until sugar dissolves. Add chocolate and stir until smooth. Remove chocolate mixture from heat.
With electric mixer, whisk eggs and yolks in a large bowl until they triple in volume and form ribbons when lifted. Whisk into chocolate mixture. Pour batter into prepared pan. Place pan on heavy baking sheet. Bake until edges puff and crack slightly, but centre is not completely set (about 1 hour); do not over bake (cake will set as it cools). Transfer to rack and cool. Cover and refrigerate overnight.
Run a small sharp knife around cake pan sides to loosen. Carefully release pan sides. Place on platter and serve in small portions.