Place half the cookies face down on a baking sheet. Top each with a large spoonful of ice cream, and then another cookie. Put the pan into the freezer for about 30 minutes to set the ice cream.
Meanwhile, melt the chocolate. Put half the chips in a bowl and microwave in 30 second intervals, stirring after each, until melted. Stir in the other half of the chocolate until melted, then stir in the espresso powder. Transfer the chocolate to a plastic bag.
When the sandwiches have set, snip a tiny bit off one corner of the plastic bag. Working a few sandwiches at a time, drizzle them with chocolate and sprinkle with the salt. It's important to alternate these two tasks, otherwise the chocolate will start to freeze onto the cookies and the salt won't stick to it. Put the sandwiches back into the freezer for 30 minutes or so for the ice cream to set fully. To store for longer, wrap each sandwich individually in plastic wrap, then put them in a large plastic bag in the freezer.