*Pedant alert* Mushy peas are actually made from marrowfat peas.
After years of being denied them in New Zealand (they aren't a thing here, apart from tinned Batchelor's ones in the supermarket) I was talking to my neighbour - a plant technologist - who happened to mention she was testing batches of marrowfat peas at work for a grower. Apparently they grow tons of them here but most of the crop gets exported to the US and Canada for processing into soup mixes. I asked her if she could perhaps get hold of some so I could show her what real mushy peas should taste like. Lo and behold, she turned up a couple of days later with a 25kg sack of them!! 5 years later and I'm still using them.