This elegant monochromatic cake gets its hue from brown-sugar buttercream. The design is first sketched with a skewer, then stems, buds and leaves are made. Piped roses are placed last.
Trim the tops of the cakes with a long serrated knife to make the surfaces level. With a small offset spatula, spread top of bottom cake layer with 1 1/4 cups frosting. Place the second cake layer, cut side down, on top of the first cake layer
Gently brush away loose crumbs from top and sides of cake with a pastry brush. With the offset spatula, spread about 2 cups frosting over top and sides of cake to form a crumb coat. Refrigerate cake until frosting is firm, about 15 minutes.
With a large offset spatula, spread about 2 more cups frosting over top and sides to form a second coat. Smooth top and remove excess frosting with the large offset spatula. Smooth sides with a bench scraper. Return cake to refrigerator, and chill until second coat is firm, about 15 minutes.
Decorate cake: Using a toothpick or wooden skewer, mark a pattern on the frosting to serve as a guideline for piping stems. Pipe stems, using the #3 round tip, on the cake. With the #103 petal tip, make one petal. Make a second, smaller petal on top of the first. Pipe a strip of frosting from left to right over the base of the two petals. Repeat, from right to left, angling the tip slightly away from the bud, releasing pressure at the end. With the #352 leaf tip, make leaves at the bud's base. Switch to the #3 tip to fill in under the leaves and connect to stems. Pipe dots against the stem, pulling off at an angle for thorns. To make leaves for large roses, switch to the #70 leaf tip. Hold the bag at a 45 degree angle to the cake with the tip's flat side up. Squeeze bag, and pull out from the base of the leaf, releasing pressure and lifting to form the end.
Pipe rosebuds: You'll need a "flower nail" (we used a #7), available in baking-supply stores, to make roses. (When you need both hands to switch tips or colors, anchor the nail in a block of floral foam or in a potato with a flat-cut bottom.) Dab frosting on the top of the nail to secure a small square of parchment paper on top. Using the #12 round tip, squeeze bag gently and pull up slowly to make an acorn shape on top of the parchment. Switch to the #103 petal tip. Holding tip against the point of the acorn, wide end down and the narrow end angled in toward the acorn's center, pipe a wide strip as you turn the nail, enrobing the top completely. Turning the nail as you go, make two slightly arched petals that each reach around half of the circumference of the acorn. Continue turning the nail, making longer petals that overlap, until you reach the bottom of the rose. Gently slide the parchment with the rose off the nail and onto a baking sheet, and refrigerate about twenty minutes; use a small offset spatula to transfer roses to the top of a cake.
Transfer cake to a serving platter. Arrange roses on cake. Fit a pastry bag with the #5 round tip, and fill with frosting. Make a border at bottom of cake: Pipe overlapping teardrop shapes (to resemble thorns) by applying pressure quickly and releasing as you pull away.
Refrigerate cake until ready to serve. Let stand at room temperature 20 minutes before serving. Slice into wedges: To avoid crumbs on surface, make each cut with one downward motion, pulling knife back toward you (not upward) and wiping knife clean after each cut.
Cake can be refrigerated for up to four hours.