Getting a Visa is a pretty hard thing to do, especially if you're going there for something like pastry-making.
But I assume that if you visit Japan and go to as many businesses as possible and have them sample you're pastries, and if by some stroke of luck they are just tasty enough, they may just sponsor you and help you get a visa. That seems unlikely because I'm sure there are tons of Japanese chefs... I'm not sure though, maybe someone has worked in the field.
