Preparation Sift cocoa into medium bowl. Bring cream and ground coffee to boil in heavy small saucepan, stirring to blend. Remove from heat; cover and steep 10 minutes. Strain cream through fine sieve into another bowl, pressing on coffee grounds to release as much cream as possible. Bring sugar, corn syrup, 1/4 cup water, and coffee-flavored cream to boil in medium saucepan, whisking until sugar dissolves. Boil 1 minute, brushing down sides of pan with wet pastry brush. Remove from heat. Whisk in chocolate, butter, and vanilla. Pour 1/4 of chocolate mixture into cocoa to moisten, then add remaining chocolate mixture, whisking until sauce is smooth and shiny. DO AHEAD Can be made 1 week ahead.Cool. Cover and refrigerate. Rewarm sauce over low heat before using.
Preparation Sift cocoa into medium bowl. Bring cream and ground coffee to boil in heavy small saucepan, stirring to blend. Remove from heat; cover and steep 10 minutes. Strain cream through fine sieve into another bowl, pressing on coffee grounds to release as much cream as possible. Bring sugar, corn syrup, 1/4 cup water, and coffee-flavored cream to boil in medium saucepan, whisking until sugar dissolves. Boil 1 minute, brushing down sides of pan with wet pastry brush. Remove from heat. Whisk in chocolate, butter, and vanilla. Pour 1/4 of chocolate mixture into cocoa to moisten, then add remaining chocolate mixture, whisking until sauce is smooth and shiny. DO AHEAD Can be made 1 week ahead.Cool. Cover and refrigerate. Rewarm sauce over low heat before using.