Place racks in upper and lower thirds of oven; preheat to 350°.
Place ¾ cup (82.5 g) powdered sugar in a small bowl; set aside.
Mix 4 oz. mascarpone, ½ cup (1 stick) unsalted butter, and remaining ¾ cup (82.5 g) powdered sugar in a large bowl with a rubber spatula or wooden spoon until combined and a little lighter in color, about 1 minute.
Mix in 2 Tbsp. Kahlúa or other coffee liqueur (if using), 1 Tbsp. vanilla bean paste or extract, and 1 tsp kosher salt.
Add 2 Tbsp freshly brewed espresso (or mix instant espresso with water), (increase water to 4 Tbsp. if not using coffee liqueur).
Stir into mascarpone mixture to combine. Using a hand-held whisk, beat the mixture to break down any visible large clumps (1 min) (The mixture will not be smooth but you don’t want large chunks of butter and mascarpone).
Sift in 2 cups (250 g) all-purpose flour, 1 tsp. baking powder, and ¼ tsp. ground cinnamon and carefully mix until no dry floury spots remain. Cover dough with plastic wrap and chill in refrigerator 20 minutes.
Scoop out 1-tablespoonful portions of dough; roll into smooth balls.
Divide between 2 parchment-lined baking sheets, spacing about 2" apart.
Bake cookies, rotating baking sheets top to bottom and front to back halfway through, until slightly puffed, golden underneath, and dry to the touch, 13–15 minutes.
Let cool on baking sheets 15 minutes.
Working one at a time, roll cookies in reserved powdered sugar to coat, placing back on baking sheets as you go.
Just before serving, roll cookies in powdered sugar again, returning to baking sheets.
Place ¼ cup Dutch-process cocoa powder in a small fine-mesh sieve and dust cookies.
See notes for storage and advance prep instructions