For the cake: Preheat oven to 350 degrees. Butter a 9-by-3-inch round cake pan. Line with parchment, and butter parchment.
Bring water to a boil in a saucepan. Meanwhile, combine dates, brandy, coffee, and 2 tablespoons cocoa in a heatproof bowl. Stir in boiling water. Let cool, stirring occasionally. Puree cooled date mixture in a food processor (you should have about 2 1/2 cups). Place 3/4 cup puree in a small bowl, and press plastic wrap directly on surface; reserve. Place remaining puree in a large bowl.
Whisk flour, salt, cinnamon, and remaining 2 tablespoons cocoa in a bowl.
Beat butter and dark-brown sugar with a mixer on medium speed until fluffy. Add eggs, one at a time, beating after each addition (batter will look curdled).
Stir baking soda into reserved uncovered date puree. On low speed, beat flour mixture into egg mixture in 2 additions, alternating with the date mixture. Beat in chocolate. Transfer batter to prepared pan, and smooth top.
Bake until a toothpick inserted into center of cake comes out clean, about 1 hour. Let cool in pan on a wire rack for 30 minutes. Run a knife around edge of pan to loosen, and invert cake onto rack. Remove parchment, turn cake right side up, and let cool completely. (Cake can be wrapped in plastic and stored at room temperature for up to 2 days.)
Make the glaze: Bring butter, light-brown sugar, corn syrup, water, and salt to a boil in a saucepan over medium-low heat, stirring occasionally. Boil 3 minutes. Remove from heat. Whisk in cream. Add chocolate, and whisk until smooth. Whisk in brandy. Let cool until thickened, 15 to 20 minutes.
Assemble the cake: Using a serrated knife, trim rounded top of cake so it is flat. Place cake on stand. Spread remaining 3/4 cup date puree over top of cake. Pour glaze over top, letting some drip down sides. Garnish with halved dates.