This dessert is meant to be casual: Serve yourself, your significant other or whomever else you’re sharing home quarantine with at leisure. I used a shallow dinner bowl but any 4-cup dish will work. If you don’t have heavy cream already at home, or there is none at the grocery, you can use 1/2 cup of plain Greek yogurt or sour cream (no need to whip it); use whipped topping, such as Cool Whip (I won’t judge!) in place of the whipped cream; or, to make it vegan, use whipped canned coconut cream. And if you don’t have both granulated and brown sugar, use 2/3 cup total of whatever you have. Same goes for the chocolate chips; if you have leftover bars, use those instead.
In the bowl of a stand mixer or large bowl, combine both sugars, the instant espresso, vanilla, salt and 1/3 cup boiling water. Attach the whisk attachment to the mixer, or use a handheld mixer, and beat on medium-low speed until the ingredients are combined and starting to thicken, 1 to 2 minutes. Increase the speed to medium-high and continue beating until the mixture is lightened and the consistency of shaving cream, 3 to 4 minutes more.
Turn off the mixer and pour in the chocolate. Continue beating on medium speed until the chocolate combines with the coffee fluff. The mixture will deflate slightly and that’s OK. Scrape the whisk and bottom of the bowl to make sure everything is combined evenly, then transfer the mousse to a bowl. Pour the cream into the mixer (no need to clean the bowl or whisk) and beat it on medium speed until stiff peaks form. Scrape the whipped cream into the mousse and gently fold the two mixtures together until smooth.
Place enough ladyfingers in the bottom of any shallow 4-cup dish to cover it, breaking the cookies into pieces to fit. Pour over half the mousse, then cover with the remaining ladyfingers, or enough to cover (you may have leftover ladyfingers, depending on the size and brand you’re using). Scrape the remaining mousse over the ladyfingers and use a small metal spatula or spoon to spread the mousse evenly across so that it covers the ladyfingers completely. Transfer the dish to the refrigerator and let chill until set, at least 4 hours or up to overnight.
Dust some cocoa powder and/or powdered sugar over the top of the tiramisu, if you like, then dig in.