To make the cake: Preheat the oven to 325 degrees F. Spray a bundt pan with cooking spray, then dust with flour, tapping out the excess. In a large heat-proof bowl, pour the hot coffee over the butter and bittersweet chocolate. Stir until blended, then set aside for 10 minutes to cool.
Add the beaten eggs and vanilla. Sift the flour, cocoa, sugar, baking soda, and salt together, then whisk into the chocolate mixture. Stir in the instant coffee, and pour into prepared pan. Bake for about 55 minutes, or until cake tests done. Cool o a rack, then turn out onto a cake board or plate.