Simply summon a falling block as a passenger on top of another one, and it will break off into an item. To see this effect yourself, use this command:

/summon falling_block ~ ~ ~ {Time:1,Passengers:[{id:"minecraft:falling_block",Time:1,BlockState:{Name:"minecraft:command_block"}}],BlockState:{Name:"minecraft:command_block"}}

I sincerely hope this was not intentional.