Remove ice cream from freezer and leave at room temperature to soften a little, about 10 min. Meanwhile, put kettle on to boil. Place sugar and instant coffee granules in a medium bowl, then dissolve by stirring in 3 tbsp (45 mL) boiling water. Then add mascarpone and whisk until evenly mixed. (Mixture will not be smooth.)
Once ice cream is soft enough, scoop into bottom of a 9×13-in. (3-L) baking dish. Using back of ice cream scoop or spoon, press down until fairly smooth. Break cookies into small chunks, scattering evenly over ice cream, then gently press into ice cream. Drizzle Kahlua over cookies. Scrape mascarpone mixture over top. Using a rubber spatula or a spoon, smooth top as best you can. Cover with plastic wrap. Freeze at least 4 hours, preferably overnight. Or over-wrap with foil and freeze up to 1 week.
When ready to serve, soften slightly by letting stand at room temperature 8 to 10 min. Slice into serving-size pieces and place on plates. Spoon cocoa into a small sieve. Gently shake over each piece of tiramisu to lightly dust. Serve immediately.
Nutrition (per serving)
We used coffee-flavoured ice cream and replaced ladyfingers with biscotti to give this classic a contemporary twist.