Cut a large piece of thin acetate into strips that are 5 inches wide and as long as one side of each of the tiers (you will need 4 strips of each length per tier). Place a strip on a clean work surface with a short side facing you. Coat surface of wood-graining tool with a thick layer of white chocolate. Starting at top of acetate strip, rock coated tool back and forth while dragging it in one swift motion to make a vertical striation. Transfer acetate, chocolate side up, to an upside-down rimmed baking sheet; refrigerate until set, about 6 minutes.Advertisement
Meanwhile, temper bittersweet chocolate: Melt 2/3 of the chocolate in a heatproof bowl set over a pan of barely simmering water until it registers 118 degrees on a candy thermometer. Remove bowl from heat, and add remaining chocolate to the bowl; stir with a rubber spatula until chocolate cools to 84 degrees. Remove any unmelted pieces; discard. Return bowl to pan; stir until chocolate reaches 88 degrees to 90 degrees.
Immediately transfer acetate to work surface; pour bittersweet chocolate on top. Quickly spread evenly over the entire surface with an offset spatula (do not spread it too much or white chocolate will smear). Use immediately.
You will need sheets of thin acetate for this project -- you can find these at baking and art supply stores alike.