I spent a few days farming eggs and buying out every Mageroyal and Small Egg on the AH. I'd been discussing this whole plan with a guildmate who ran off to the Silvermoon sweet spot and farmed over 200 eggs in under an hour and spent the days following farming Mageroyal.
Total I had 21 cakes ready to sell on Sunday morning and I posted 10 of them at 100g each at roughly 00:45 before going AFK to play Final Fantasy XIII for a few hours. Returning at 07:00, only one cake had sold, much to my chagrin. Seems I missed the huge undercutting war that broke out but I was now the only one with cakes on the AH and they began to steadily sell with six more flying off the shelf in the span of thirty minutes. Wanting to see what the market was willing to pay, I canceled all of and relisted half of my cakes at 200g each; only three sold during a one-hour span before the undercutting began anew. I also began listing Mageroyal in stacks of 3 for 50g.
My cakes were undercut at 75g but I was certain that no one had a supply of hundreds of cakes, I canceled and reposted at 100g each and took a nap. On returning, all of the cakes had sold and prices were back up so I listed more at 100g each before being undercut again. My guildmate and I agreed to whitelist each other unless the competition started getting nasty on undercuts and the market bombed.
I did not realize that the Lovely Cakes had a thirty-minute cooldown or I'd have started this two days ago, but the profit from these were quite nice. The cake from a vendor cost me 14g40s (Exalted rep) and makes five slices. I turned around and sold each slice for 10g, making about 33g profit from each whole cake after AH fees. A few others caught on but the slices sold rather consistently all day.
I did not bother with the Tasty Cupcake or other markets. My guildmate had success selling the spices and flour in proper stack-sizes for crafting. By yesterday afternoon we had each made over 2000g with more potential on the horizon.
Sunday would have been the big rush day for this as the achievement is one of the easiest to obtain and a large population of people are online then. Monday (today) should be fairly steady in demand as those who don't play on Sunday log in and with a general lack of Monday raids folks have nothing better to do. Tuesday through probably Thursday the demand will be lessened as most folks will have completed the achievement already, but those PvPing on the AH will also be lessened as many will be raiding. Friday may see an increase among the 9-to-5 crowd and folks working on alts, while Saturday will see the last-ditch rush of folks trying to complete before the event is over. Saturday will be hit-or-miss, depending on how many people still have stock; if everyone still has plenty, prices will plummet as everyone tries to ditch, but if most of the contenders are sold out, the person with the last small supply could pull in a large amount of gold from the desperate.