How to Make It
Line a 9-by-5-inch loaf pan with foil, allowing 2 inches of overhang on all sides. In a stainless steel bowl set over a saucepan of simmering water, melt the chocolate in the coconut oil, stirring, 7 minutes. Whisk in the cocoa powder, vanilla and salt until incorporated, then whisk in the cream until smooth. Let cool slightly.
Pour a 1/4-inch-thick, even layer of the ganache into the prepared pan. Arrange a layer of biscuits on the ganache, breaking them to fit and leaving a 1/4-inch border of ganache around the edge. Repeat the layering with the remaining ganache and biscuits, ending with a layer of ganache.
Cover the pan with plastic wrap and refrigerate until chilled, 3 hours. Let stand at room temperature for 30 minutes. Using the foil, lift out the cake onto a cutting board. Discard the foil and slice the cake crosswise 3/4 inch thick. Serve with whipped cream, if desired.