Line 11.5 x 4 x 4-inch rectangular frame mold with acetate sheet. You may have to tape two acetate sheets together to accommodate the height of the mold. Set lined mold over rectangular cake board or small baking sheet.
Dip each ladyfinger in warm match marsala syrup for 2-3 seconds on each side. Do not soak the ladyfinger, otherwise it will soften too much. Place a row of 10 dipped ladyfingers in bottom of prepared mold.
Spread a rounded 1 cup of matcha mascarpone filling in an even layer over ladyfingers. Repeat second layer of dipped ladyfingers, followed with another rounded cup of filling. Add third layer of dipped ladyfingers and finish with remaining matcha mascarpone filling. Smooth the top layer using the back of a spoon or a mini offset spatula.
Cover assembled tiramisu with plastic wrap. Let chill in the fridge for at least 2 hours, up to overnight. Remove plastic wrap. Gently remove metal frame mold and gently remove acetate sheet from tiramisu.
In a small bowl, combine powdered sugar and matcha powder. Dust the surface of matcha tiramisu with matcha sugar mixture using a sifter. Use a serrated knife or chef's knife to slice tiramisu into individual servings.
Serve matcha tiramisu cold or at room temperature.