Line an 8-by-4-by-3-inch loaf pan with plastic wrap, leaving enough overhang in each direction to completely cover the top. Line the bottom and sides of the pan with chocolate wafers and set aside.
Sprinkle the gelatin over 1/4 cup cold water in a small saucepan (or even a metal measuring cup) and "bloom" at room temperature for 5 minutes. Then gently warm over low heat until just melted. (Do not allow to boil.) Remove from the heat and stir in the coffee liqueur, espresso powder and vanilla.
Whip the heavy cream, powdered sugar and salt in the bowl of a stand mixer on high until soft peaks form, about 1 minute 30 seconds. Reduce the speed to low and drizzle in the cooled gelatin mixture. Increase the speed back to high and whip to stiff peaks, about 30 seconds more.
Fill the prepared pan 3/4 of the way with the whipped cream mixture. Insert the remaining chocolate wafers vertically (edge first) into the whipped cream to create 4 rows of about 12 cookies each, keeping each cookie slightly separated by cream.
Spread the remaining whipped cream evenly over the cookie rows. Fold the excess plastic wrap over the cake and refrigerate for at least 8 hours and up to 24.
To serve: Pull back the plastic wrap and invert the cake onto a serving dish. Remove the plastic wrap, slice and serve immediately.