PREP: See Note 1. Set coffee mixture aside in a shallow bowl that has plenty of room to dip the entire cookie at once. Lightly grease an 8x8-inch pan with cooking spray, set aside for now. Separate 3 eggs -- yolks from whites. Add yolks to a bowl attached to a stand mixer and whites to a separate bowl for now. Take the mascarpone out of the fridge.
EGG YOLKS: Pour sugar on top of the egg yolks. Attach whisk attachment and beat at high speed for 6 for 10 minutes or until it color changes to a very light (almost white) yellow and becomes quite thick. Scrape sides occasionally as needed. Turn off mixer then use a spatula to scrape in all of the mascarpone. Add in vanilla paste or extract. Beat on low speed just until combined and smooth. Use a spatula to scrape all of this mixture to a separate very large bowl.
CREAM: No need to clean out stand mixer bowl or whisk yet. To the stand mixer bowl, add in heavy cream (cold--straight from the fridge) and beat, still with whisk attachment, at high speed 6 for 3 minutes or until medium peaks form (not soft, but not stiff/hard -- here's a helpful graphic). Be careful to not over-beat. Use a spatula to gently mix the cream into the egg yolk mixture. Now wash out the stand mixer bowl and whisk being sure to thoroughly dry both. EGG WHITES: Add egg whites and salt to stand mixer bowl. Beat on high speed 6 until eggs are stiff, bright white, and foamy, about 2-3 minutes. Add 1/2 of the egg whites to the cream mixture and very gently fold into the mixture with a spatula. When mostly incorporated, add the rest of the egg whites and again very gently fold the egg whites into the mixture to combine.
DIP COOKIES: If using, add in the liquor to the coffee and stir. Very quickly dip one cookie at a time in the mixture (don't soak at all!) and then place in the pan. Line the base of the pan, breaking cookies apart to fit if needed.
ARRANGE: Spread half the cream mixture on top. Through a fine mesh sieve, sprinkle Sift 1/2 tablespoon cocoa powder through a fine-mesh sieve onto the top. Then repeat -- cookies dipped in coffee followed by the remaining cream mixture. Cover tightly with plastic wrap and place in the fridge for 6-8 hours, preferably overnight.
ENJOY: Right before serving, sprinkle the remaining 1/2 tablespoon cocoa powder on top through a fine mesh sieve. Cut into pieces, serve, and enjoy! (To get clean cuts: use a sharp knife. Run the knife under hot water, quickly dry it off, and then make a cut. Repeat for each cut.)