The Blockbuster evolved into three types. The first was the 4000lb cookie which was first used in January 1941. Then you had the 8000lb and finally the 12000lb Blockbuster. The latter came in three bolt on sections. Be careful on this one because they were not three cookies bolted together it was three different segments.
These bombs are often credited to Barnes Wallis but in fact if you find a drawing of the BM1000 parachute mine the weapons are identical.
The last cookies used were dropped by Number 1 Squadron RAAF in the Firedog operation in 1955. They needed the governor generals permission to use them over Malaya. The Boeing Washington reputidly carried a load of cookies in the air exercises in the 1950's. They were called cookies because when they went to be filled at the ordnance depot the driver thought they were part of a cooking device and took the mines to the cookhouse.
They were called Blockbusters because they blew down blocks of houses