Stir 1 tablespoon of the espresso powder into the coffee liqueur in a liquid measuring cup until dissolved. Set aside.
Combine the mascarpone and confectioners' sugar in the bowl of a stand mixer fitted with a paddle attachment on low speed until just combined, about 15 seconds. With the mixer on low, slowly pour in the liqueur-espresso mixture followed by the cream and continue to whip until all the liquid is incorporated. Increase the mixer to medium speed and continue to whip until the mascarpone-cream mixture reaches a medium-stiff peak, about 1 minute. Set aside.
Stir together the vodka, granulated sugar, remaining 2 tablespoons espresso powder and 3/4 cup hot water in a small bowl until the sugar and espresso powder are dissolved.
Fill the bottom third of each of four 7- to 7 1/2-ounce martini glasses with some of the mascarpone cream and smooth with the back of a spoon. Dip 1 ladyfinger half at a time into the espresso mixture for 2 seconds per side, until soaked but not soggy. Arrange 2 soaked ladyfinger halves over the cream in each glass. Spoon more mascarpone cream on top of the ladyfingers to fill the next third of the glass and smooth with the back of the spoon. Individually dip 3 more ladyfinger halves for 2 seconds per side and arrange on top of the mascarpone cream. Top each martini glass off with the remaining mascarpone cream. Use a small offset spatula to smooth and level off the tops of each glass. Loosely cover each glass with plastic wrap and refrigerate for 4 hours.
Remove the martini glasses from the refrigerator. Place a small square of parchment over half of a glass. Sift a generous amount of the cocoa powder through a fine-mesh sieve over the exposed half. Remove the parchment. Repeat with the remaining 3 glasses. Serve with 3 chocolate-covered espresso beans in the center of each glass.
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