The magical dessert in question is called honey toast!
The legend behind exactly where honey toast started is a bit up in the air. There is a theory that it started in a karaoke bar in Sapporo - but there's no real confirmation as to whether or not this was definitely the first instance of the dessert.
If you'd like to try honey toast while you're visiting Tokyo, there's an easy place where you can - called the Honey Toast Cafe, in Akihabara. Akihabara is a fun spot to visit anyway - particularly if you're into electronics, anime and manga, or want to check out a maid cafe - but adding some honey toast into your day there might be the perfect way to cap things off!
- Cut the hollowed out section into cubes and bake it all with butter and honey (or sometimes maple syrup)
You can find the Honey Toast Cafe at 1 Chome-1-10 Sotokanda, Chiyoda, Tokyo 101-0021, not far at all from the Akihabara Station (about 5 minutes on foot). There are also other places selling the dessert - I've walked past places in both Shinjuku and Shibuya that have it on their menu boards. The only word of warning that I'd offer is that they are as huge as the pictures would suggest - so sharing them with a friend (or several) is a good idea!