Make the mint cream: With an electric mixer, beat heavy cream, sugar, and mint extract until stiff peaks form.
Line a serving platter with two sheets of wax paper side by side. Assemble the cake: Spread each wafer with about 1/2 tablespoon mint cream, forming stacks. Lay stacks horizontally along seam of paper, pressing gently to form a log. With small spatula or knife, cover log with remaining mint cream. Refrigerate at least 4 hours or up to 2 days.
To serve, gently remove wax paper from underneath cake (holding cake in place with a metal spatula, if necessary), and sprinkle with chocolate chips. Slice cake diagonally with a serrated knife.