Lightly butter two 6-oz. ramekins and dust with granulated sugar, tapping out excess. Set the ramekins on a small baking sheet.
Stir together the liquor or water and the espresso powder. Set aside and stir occasionally until the coffee is dissolved. Melt the chocolate and butter in a medium metal bowl over a pan of simmering water or in a microwave. Remove from the heat and whisk until glossy and smooth. Stir in the coffee mixture and the salt. Whisk in the egg yolk. Add about one-third of the confectioners' sugar and whisk until well blended and smooth. Set aside.
In a medium bowl, beat the egg white with an electric mixer on medium-high speed until it's very foamy and they're just beginning to hold soft peaks. Increase the speed to high and gradually sprinkle in the remaining confectioners' sugar. Continue beating until the peaks are firm and glossy. Spoon about one-quarter of the beaten whites into the chocolate mixture and whisk until blended. Add the remaining whites and gently fold them in until just blended. Pour evenly into prepared ramekins (the mixture will almost completely fill the ramekins). If you want to bake the soufflés within 24 hours, refrigerate them. (To refrigerate: Chill for about 30 minutes, and then cover in plastic and return to the refrigerator for up to 24 hours.) If you want to hold them for longer, freeze them according to the make-ahead tips below.
Heat the oven to 400°F. Unwrap the ramekins, set them on a baking sheet, and bake until they're puffed and risen about 1 inch above the ramekin, 15 minutes. The top will still be slightly sunken in the center; consider it a place to pop in a few berries or a dollop of whipped cream. Remove the soufflés from the oven and serve immediately.
Make Ahead Tips
Put the filled ramekins into the freezer, uncovered, for 20 min. Then wrap each ramekin well in plastic and freeze for up to two weeks. To bake straight from the freezer, unwrap the ramekins and set on a small baking sheet or jellyroll pan. Let them sit for 20 min. while heating the oven to 400°F. Bake on the baking sheet until puffed and risen about 1 inch above the ramekin, 18 min. Remove from the oven and serve immediately.
Photo: Scott Phillips