Green Granite, spot on.
The 'cookie' was a land mine. In basic form it was a thin metal cannister and nominally 4 000lb. Bolt 2 or 3 together and you got a real bnag.
At East Kirkby they have a couple on a bomb trolley. These bombs do not have tail fins.
I read a secret report of a secret German report. They correctly identified the 12 000lb bombs both Tall Boy and Land Mine but did not realise they were actually quite different aerodynamically. Their report quoted the one bomb being dropped from over 12 000 feet and as low as 50 feet.
Not quite sure why they got it that wrong.
The 1 000lb GP Bomb is designated as a Medium capacity weapon ie its case and explosive are about 50-50 and it is designed as blast, frag, shock whatever. A land mine OTOH has a case nearer 20% of its total weight and is designated as High Capacity.
I seem to recall, from East Kirkby, that they had rather more fuses than a simple nose/tail. Possibly because its probablity of exploding with one nose fuse, given its low impact velocity, would be low. The additional fuses possibly included anti-tamper devices.
In our use their main purpose was to flatten buildings thus exposing timber and flamable materials to air and the incendiaries.