I knew right away when I saw this task that I wanted my clues to lead to a delicious cake. Don't ask why, but somehow it just felt right. Obviously, if one is leaving clues, they don't have to lead anywhere in particular, but I felt the world would be a better place if more mysterious clues led to cake.
My original plan was to leave the cake somewhere public so a stranger would be pleasantly surprised by it, but I realized that people would be afraid to eat a strange cake that happened to be sitting out in a public place, or worse, apparently hidden.
So I ended up hiding the cake in my house for my little brother and my mother to find. This had the added benefit that I got to eat some of the cake, too.

I waited for them to go swimming, then I baked the cake while they were gone. I am not a very good cook, but this is an extremely easy recipe, and I've done it many times before, so I had it in the oven pretty quickly.
While it baked, the real work began. I had to make some clues. At this point, all I knew was that the dirty dishes in the sink would be the first clue.


I started fiddling around and I decided it would be pretty cool if I hid the ingredients and had my family follow them to find the cake. But literally as I began hiding them, I realized that it would be a lot easier if they had some sort of riddle to help them find the next one.
I am all sorts of crap at writing riddles, so I basically just wrote vague hints instead.
Then, to get them started, I tucked a note into the cookbook, which read "I baked a cake, but it escaped! Track down the rogue ingredients to find my missing meal." Which sounds like the opening to a dreadful children's computer game of the "educational" variety.
I left the cookbook out on the counter with the note sticking out conspicuously.
Once the cake had cooled, I put it on a plate and moved it into the old cupboard that used to be in our study, which we recently emptied and moved into the hall. Since it was empty, I figured it was a great place to hide the cake.

It turns out I overestimated my mother's ability to notice unusual things in her environment. It took several minutes for her to notice the dishes in the sink, and after that she put the cookbook away without seeing the note. I had to get it back out and show it to her in the interests of moving the game along.
After that, my little brother got involved and things moved along better.

The first paper clue was attached to the flour:

Which led them to the cocoa powder, hiding in the towel closet:

The salt was on top of the CD rack:

The vanilla hid amongst the sake jars:

The baking powder was snuggled up with my mother's stuffed penguin:

The eggs were in the fridge, because I was afraid they would break if I hid them:

The butter was inside a cornucopia we use as a centerpiece on the eight festivals of the Wheel of the Year:

The sugar jar was on top of the fridge, which is black (hence "a black shelf"):


And finally, they found the cake:


And there was much rejoicing.