For those who cleared the entire eventstore except for the pile of gold: don't go after the pile of gold, but invest in more tea sets!
The 5th boss *always* has a gold reward, the lowest is 15,000 gold.
Tea Sets cost at most 600 Fruit Tarts a piece.
15,000 gold from the goldpile costs 15,000 Fruit Tarts
15,000 Fruit Tarts / 600 Fruit Tarts per Tea Set = 25 Tea Sets

Now it depends a bit on how many Tea Sets you need to take down the event boss, but I bet you need less than 25 Tea Sets.
If you need as many as 10 Tea Sets to take down that boss, then that still rewards at least 2.5 * 15,000 = 37,500 gold.
If you need only 2 Tea Sets to take down that boss, then the reward is at least 12.5 * 15,000 = 187,500 gold.