2. If a cake doesn't bake level -- they often don't -- even it out with a serrated knife. Use a turntable to make it even all around.
3. Place a small dollop of the buttercream in the center of the cake. Put another foam-board round on top of the tier; invert the cake onto the foam board. Remove the original foam-board base and parchment. The bottom of the cake is now the top; the cake will remain on this foam-board round from now on.
4. Split the cake. Hold a serrated knife against the edge of the cake; rotate the turntable, working the knife through the cake.
5. Brush the cut surface of the bottom half of the cake with a sugar syrup, flavored with liqueur or orange zest if desired. This syrup will moisten the cake and add a subtle flavor.
6. Pipe the buttercream around the perimeter of the bottom half of the cake. Use a pastry bag fitted with a standard-size coupler. This "dam" will keep the jam filling in place.
7. Fill the bottom layer with jam filling one-eighth of an inch thick; don't use so much that the top layer slips and slides.
8. Carefully replace the top layer, cut side down, and brush with sugar syrup. Then let set for 2 to 3 minutes.
9. Ice the top with buttercream using an offset spatula to give the tier a "crumb coat." This thin layer of icing will seal the cake. Start from the center and work out, making sure to push the buttercream over the sides of the tier.
11. Give the tiers a final coating of buttercream. Use an offset spatula to smooth the top, and a tool called a bench scraper for the sides. Before you ice each tier, wipe off the spatula, dip it in hot water, then wipe it off again; using the warm, clean spatula will make a clean, finished edge.
12. The icing should be smooth and uniform. But perfection is nearly impossible; if you see an air bubble or other small flaw, make that side the back of the cake. Refrigerate the tiers.
13. Prepare the cake board at least eight hours before assembling the cake. It should be at least 4 inches wider than the cake and strong enough to support its weight, which for this 4-tier cake can easily exceed 50 pounds. Boards are available at baking-supply stores; this one, made of flake board, was cut for us at a hardware store. Spread a thin layer of royal icing over the cake board; it's not necessary to ice the center, but the icing must be brought to the edge of the board. Let the royal icing dry completely, at least 8 hours or overnight.
14. Insert a 1/4-inch dowel vertically into the bottom tier of the cake; mark it 3/8 of an inch above the top of the tier. Remove it, and cut 8 dowel pieces to this length. These will be the supports for the next tier. Use 5 cut dowels to form a circle an inch and a half in from the edge of the tier that will be placed on top (hold an empty cake pan over the finished tier to figure out placement); use the other 3 to form a triangle inside the circle. Repeat the process on each tier -- except the top one -- using fewer dowels in different configurations as tiers get smaller. Do not place dowels directly in center of tiers. At this point, cakes can be refrigerated overnight.
15. Assemble the cake on its serving table. Dab some royal icing onto the center of the cake board, and place the bottom tier on it. Add the next tier, resting it on the dowels; the 3/8-inch space between the tiers will hide the bases of the flowers you'll use for decorations. Once all the tiers are stacked, cut a dowel a 1/4-inch shorter than the height of the cake. Using a knife or a clean pencil sharpener, whittle one end to a point and, with a mallet, gently drive it through the center of all the cakes and foam boards. Do not hammer too close to the cake -- push the end in with your fingers.
16. Use a pastry bag fitted with a large leaf tip to pipe big, ruffly buttercream leaves along the top edges of the tiers.
17. Trim the flower stems close to the base. Use unsprayed flowers (you may want to use edible ones like violets and nasturtiums). The hydrangeas, violas, and scabiosa used on this buttercream cake are from Martha's East Hampton, New York, garden. Decorate the base of each tier with the flowers. The monogram, which sits on the top tier, is made from twenty-four-gauge wire with small sprigs of thyme wired to it.
18. Starting at the back of the cake, use a hot-glue gun to attach ribbon around the perimeter of the cake board. With this final touch, the wedding cake is now ready to be admired by the guests before being sliced by the bride and groom.