PREHEAT oven to 325° F. Grease two 8-inch-round cake pans. Line bottoms with wax paper.
COMBINE sugar, flour, baking soda and salt in large bowl. Bring coffee to simmer in small, heavy-duty saucepan. Remove from heat. Add chocolate; whisk until chocolate is melted and smooth. Cool slightly.
WHISK vegetable oil, sour cream, eggs and vanilla extract in another large bowl to blend. Add chocolate-coffee mixture; whisk to blend well. Add one-third of chocolate-sour cream mixture to dry ingredients; whisk to blend well. Add remaining chocolate-sour cream mixture in 2 more additions, whisking well after each addition. Divide batter equally between prepared pans. (Batter will be thin.)
BAKE for 33 to 35 minutes or until wooden pick inserted in centers comes out clean. Cool in pans on wire racks for 10 minutes. Run knife around edges of cakes. Invert onto wire racks; remove wax paper. Cool completely. Spread frosting between layers and over top and sides of cake. Store any leftover cake in refrigerator. Bring to room temperature before serving.
BRING cream, butter, sugar, water and salt to simmer in medium, heavy-duty saucepan over medium heat, stirring frequently. Remove from heat. Immediately add chocolate; let stand for 2 minutes. Whisk until melted and smooth. Add vanilla extract. Pour into medium bowl. Refrigerate, stirring occasionally, for about 1 1/2 hours or until thick enough to spread.