Bring cream to a boil. Remove from heat and add chocolate; allow to stand several minutes, add butter, corn syrup, liquor and whisk smooth. Cool about 2 to 3 hours at room temperature to about 80 degrees F. Beat with paddle on medium speed in electric mixer until light. Pipe out small truffles on paper with a pastry bag fitted with a 1/2-inch plain tube. Refrigerate to set for at least 1 hour.
Melt and cool or temper the chocolate. Sift the cocoa into a deep pan. Coat truffles, using your hand to cover truffles with tempered chocolate. Deposit the truffles in the cocoa as they are enrobed and shake the pan to cover them. Remove the truffles to another pan as they are coated. After the covering sets, shake the truffles in a strainer to remove the excess cocoa.