Select the Blueprint or the asset you want to carry over > Right click > Migrate > Select the other project’s Content folder > Hit OK.
That’s…great, how come one cannot just stay in the working project and use a “import” feature to select asset files and bring them into the working project…
You can leave the project you are working on open as you do the migration; assets and folders will appear in the Content Browser when migration is complete. The project you are migration from has to be open in order for the engine to find and migrate all of the dependencies as well. Otherwise you would be able to import a BP or a material but not the contents(static meshes, textures, etc.) in it.
Just to add to Jacky’s answer, its easier to migrate from an already open project to another project, the reason being that when you select “Migrate”, it will find every depenency for what it is you are trying to migrate, and it will bring that over to the Content folder that you specify for the other project. In the worst case you could always just have two processes of your editor open and you wouldn’t have to close the one you are working in just to have files migrated over.