[Silkworm]

I can recommend Bleu de Solaise.   Very hardy and doesn't bolt.

I concur with Anne B, I have grown Musselburgh and Blue de Solaise side by side for 2 years
and Blue de Solaise out grow the Musselburgh which are bolting again this year.
Blue de Solaise are about 2" in diameter, Musselburgh 1" or less.

Silky 

[conteasy]

If you don't eat all your King Richard as baby leeks they grow into fine long thicker specimens, not as fat as Musselborough but in a sheltered spot mine have survived the weather surprisingly well stuck up a foot high out of the ground!  One year I planted some spares in a short trench and earthed them up as well - they grew two feet long and were delicious!

[fatcat1955]

Oarsman or Longbow for me.